diff --git a/docs/dev/user_defined_functions.zh.md b/docs/dev/user_defined_functions.zh.md
index a1b52a087dc21..e2473afee55a2 100644
--- a/docs/dev/user_defined_functions.zh.md
+++ b/docs/dev/user_defined_functions.zh.md
@@ -1,5 +1,5 @@
 ---
-title: '用户自定义函数'
+title: '用户自定义 Functions'
 nav-id: user_defined_function
 nav-parent_id: streaming
 nav-pos: 4
@@ -23,16 +23,16 @@ specific language governing permissions and limitations
 under the License.
 -->
 
-Most operations require a user-defined function. This section lists different
-ways of how they can be specified. We also cover `Accumulators`, which can be
-used to gain insights into your Flink application.
+大多数操作都需要用户自定义 function。本节列出了实现用户自定义 function 的不同方式。还会介绍 `Accumulators`（累加器），可用于深入了解你的 Flink 应用程序。
 
 <div class="codetabs" markdown="1">
 <div data-lang="java" markdown="1">
 
-## Implementing an interface
+<a name="implementing-an-interface"></a>
 
-The most basic way is to implement one of the provided interfaces:
+## 实现接口
+
+最基本的方法是实现提供的接口：
 
 {% highlight java %}
 class MyMapFunction implements MapFunction<String, Integer> {
@@ -41,18 +41,22 @@ class MyMapFunction implements MapFunction<String, Integer> {
 data.map(new MyMapFunction());
 {% endhighlight %}
 
-## Anonymous classes
+<a name="anonymous-classes"></a>
+
+## 匿名类
 
-You can pass a function as an anonymous class:
+你可以将 function 当做匿名类传递：
 {% highlight java %}
 data.map(new MapFunction<String, Integer> () {
   public Integer map(String value) { return Integer.parseInt(value); }
 });
 {% endhighlight %}
 
+<a name="java-8-lambdas"></a>
+
 ## Java 8 Lambdas
 
-Flink also supports Java 8 Lambdas in the Java API.
+Flink 在 Java API 中还支持 Java 8 Lambdas 表达式。
 
 {% highlight java %}
 data.filter(s -> s.startsWith("http://"));
@@ -62,10 +66,11 @@ data.filter(s -> s.startsWith("http://"));
 data.reduce((i1,i2) -> i1 + i2);
 {% endhighlight %}
 
+<a name="rich-functions"></a>
+
 ## Rich functions
 
-All transformations that require a user-defined function can
-instead take as argument a *rich* function. For example, instead of
+所有需要用户自定义 function 的转化操作都可以将 *rich* function 作为参数。例如，你可以将下面代码
 
 {% highlight java %}
 class MyMapFunction implements MapFunction<String, Integer> {
@@ -73,7 +78,7 @@ class MyMapFunction implements MapFunction<String, Integer> {
 };
 {% endhighlight %}
 
-you can write
+替换成
 
 {% highlight java %}
 class MyMapFunction extends RichMapFunction<String, Integer> {
@@ -81,13 +86,13 @@ class MyMapFunction extends RichMapFunction<String, Integer> {
 };
 {% endhighlight %}
 
-and pass the function as usual to a `map` transformation:
+并将 function 照常传递给 `map` transformation:
 
 {% highlight java %}
 data.map(new MyMapFunction());
 {% endhighlight %}
 
-Rich functions can also be defined as an anonymous class:
+Rich functions 也可以定义成匿名类：
 {% highlight java %}
 data.map (new RichMapFunction<String, Integer>() {
   public Integer map(String value) { return Integer.parseInt(value); }
@@ -97,11 +102,11 @@ data.map (new RichMapFunction<String, Integer>() {
 </div>
 <div data-lang="scala" markdown="1">
 
+<a name="lambda-functions"></a>
 
 ## Lambda Functions
 
-As already seen in previous examples all operations accept lambda functions for describing
-the operation:
+正如你在上面的例子中看到的，所有的操作同可以通过 lambda 表达式来描述：
 {% highlight scala %}
 val data: DataSet[String] = // [...]
 data.filter { _.startsWith("http://") }
@@ -114,16 +119,17 @@ data.reduce { (i1,i2) => i1 + i2 }
 data.reduce { _ + _ }
 {% endhighlight %}
 
+<a name="rich-functions"></a>
+
 ## Rich functions
 
-All transformations that take as argument a lambda function can
-instead take as argument a *rich* function. For example, instead of
+所有将 lambda 表达式作为参数的转化操作都可以用 *rich* function 来代替。例如，你可以将下面代码
 
 {% highlight scala %}
 data.map { x => x.toInt }
 {% endhighlight %}
 
-you can write
+替换成
 
 {% highlight scala %}
 class MyMapFunction extends RichMapFunction[String, Int] {
@@ -131,13 +137,13 @@ class MyMapFunction extends RichMapFunction[String, Int] {
 };
 {% endhighlight %}
 
-and pass the function to a `map` transformation:
+并将 function 传递给 `map` transformation:
 
 {% highlight scala %}
 data.map(new MyMapFunction())
 {% endhighlight %}
 
-Rich functions can also be defined as an anonymous class:
+Rich functions 也可以定义成匿名类:
 {% highlight scala %}
 data.map (new RichMapFunction[String, Int] {
   def map(in: String):Int = { in.toInt }
@@ -147,95 +153,78 @@ data.map (new RichMapFunction[String, Int] {
 
 </div>
 
-Rich functions provide, in addition to the user-defined function (map,
-reduce, etc), four methods: `open`, `close`, `getRuntimeContext`, and
-`setRuntimeContext`. These are useful for parameterizing the function
-(see [Passing Parameters to Functions]({{ site.baseurl }}/dev/batch/index.html#passing-parameters-to-functions)),
-creating and finalizing local state, accessing broadcast variables (see
-[Broadcast Variables]({{ site.baseurl }}/dev/batch/index.html#broadcast-variables)), and for accessing runtime
-information such as accumulators and counters (see
-[Accumulators and Counters](#accumulators--counters)), and information
-on iterations (see [Iterations]({{ site.baseurl }}/dev/batch/iterations.html)).
+除了用户自定义的 function（map，reduce 等），Rich functions 还提供了四个方法：`open`、`close`、`getRuntimeContext` 和
+`setRuntimeContext`。这些方法对于参数化 function
+（参阅 [给 function 传递参数]({% link dev/batch/index.zh.md %}#passing-parameters-to-functions)），
+创建和最终确定本地状态，访问广播变量（参阅
+[广播变量]({% link dev/batch/index.zh.md %}#broadcast-variables )），以及访问运行时信息，例如累加器和计数器（参阅
+[累加器和计数器](#accumulators--counters)），以及迭代器的相关信息（参阅 [迭代器]({% link dev/batch/iterations.zh.md %})）
+有很大作用。
 
 {% top %}
 
-## Accumulators & Counters
+<a name="accumulators--counters"></a>
 
-Accumulators are simple constructs with an **add operation** and a **final accumulated result**,
-which is available after the job ended.
+## 累加器和计数器
 
-The most straightforward accumulator is a **counter**: You can increment it using the
-```Accumulator.add(V value)``` method. At the end of the job Flink will sum up (merge) all partial
-results and send the result to the client. Accumulators are useful during debugging or if you
-quickly want to find out more about your data.
+累加器是具有**加法运算**和**最终累加结果**的一种简单结构，可在作业结束后使用。
 
-Flink currently has the following **built-in accumulators**. Each of them implements the
-{% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/Accumulator.java "Accumulator" %}
-interface.
+最简单的累加器就是**计数器**: 你可以使用
+```Accumulator.add(V value)``` 方法将其递增。在作业结束时，Flink 会汇总（合并）所有部分的结果并将其发送给客户端。
+在调试过程中或在你想快速了解有关数据更多信息时,累加器作用很大。
+
+Flink 目前有如下**内置累加器**。每个都实现了
+{% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/Accumulator.java "累加器" %}
+接口。
 
 - {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/IntCounter.java "__IntCounter__" %},
   {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/LongCounter.java "__LongCounter__" %}
-  and {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/DoubleCounter.java "__DoubleCounter__" %}:
-  See below for an example using a counter.
-- {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/Histogram.java "__Histogram__" %}:
-  A histogram implementation for a discrete number of bins. Internally it is just a map from Integer
-  to Integer. You can use this to compute distributions of values, e.g. the distribution of
-  words-per-line for a word count program.
+  和 {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/DoubleCounter.java "__DoubleCounter__" %}:
+  有关使用计数器的示例，请参见下文。
+- {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/Histogram.java "__直方图__" %}:
+  离散数量的柱状直方图实现。在内部，它只是整形到整形的映射。你可以使用它来计算值的分布，例如，单词计数程序的每行单词的分布情况。
 
-__How to use accumulators:__
+__如何使用累加器：__
 
-First you have to create an accumulator object (here a counter) in the user-defined transformation
-function where you want to use it.
+首先，在需要使用累加器的用户自定义的转换 function 中创建一个累加器对象（此处是计数器）。
 
 {% highlight java %}
 private IntCounter numLines = new IntCounter();
 {% endhighlight %}
 
-Second you have to register the accumulator object, typically in the ```open()``` method of the
-*rich* function. Here you also define the name.
+其次，你必须在 *rich* function 的 ```open()``` 方法中注册累加器对象。也可以在此处定义名称。
 
 {% highlight java %}
 getRuntimeContext().addAccumulator("num-lines", this.numLines);
 {% endhighlight %}
 
-You can now use the accumulator anywhere in the operator function, including in the ```open()``` and
-```close()``` methods.
+现在你可以在操作 function 中的任何位置（包括 ```open()``` 和 ```close()``` 方法中）使用累加器。
 
 {% highlight java %}
 this.numLines.add(1);
 {% endhighlight %}
 
-The overall result will be stored in the ```JobExecutionResult``` object which is
-returned from the `execute()` method of the execution environment
-(currently this only works if the execution waits for the
-completion of the job).
+最终整体结果会存储在由执行环境的 `execute()` 方法返回的 ```JobExecutionResult``` 对象中（当前只有等待作业完成后执行才起作用）。
 
 {% highlight java %}
 myJobExecutionResult.getAccumulatorResult("num-lines")
 {% endhighlight %}
 
-All accumulators share a single namespace per job. Thus you can use the same accumulator in
-different operator functions of your job. Flink will internally merge all accumulators with the same
-name.
+单个作业的所有累加器共享一个命名空间。因此你可以在不同的操作 function 里面使用同一个累加器。Flink 会在内部将所有具有相同名称的累加器合并起来。
 
-A note on accumulators and iterations: Currently the result of accumulators is only available after
-the overall job has ended. We plan to also make the result of the previous iteration available in the
-next iteration. You can use
-{% gh_link /flink-java/src/main/java/org/apache/flink/api/java/operators/IterativeDataSet.java#L98 "Aggregators" %}
-to compute per-iteration statistics and base the termination of iterations on such statistics.
+关于累加器和迭代的注意事项：当前累加器的结果只有在整个作业结束后才可用。我们还计划在下一次迭代中提供上一次的迭代结果。你可以使用
+{% gh_link /flink-java/src/main/java/org/apache/flink/api/java/operators/IterativeDataSet.java#L98 "聚合器" %}
+来计算每次迭代的统计信息，并基于此类统计信息来终止迭代。
 
-__Custom accumulators:__
+__定制累加器：__
 
-To implement your own accumulator you simply have to write your implementation of the Accumulator
-interface. Feel free to create a pull request if you think your custom accumulator should be shipped
-with Flink.
+要实现自己的累加器，你只需要实现累加器接口即可。如果你认为自定义累加器应随 Flink 一起提供，请尽管创建 pull request。
 
-You have the choice to implement either
+你可以选择实现
 {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/Accumulator.java "Accumulator" %}
-or {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/SimpleAccumulator.java "SimpleAccumulator" %}.
+或 {% gh_link /flink-core/src/main/java/org/apache/flink/api/common/accumulators/SimpleAccumulator.java "SimpleAccumulator" %}。
 
-```Accumulator<V,R>``` is most flexible: It defines a type ```V``` for the value to add, and a
-result type ```R``` for the final result. E.g. for a histogram, ```V``` is a number and ```R``` is
- a histogram. ```SimpleAccumulator``` is for the cases where both types are the same, e.g. for counters.
+```Accumulator<V,R>``` 的实现十分灵活: 它定义了将要添加的值类型 ```V```，并定义了最终的结果类型 ```R```。例如，对于直方图，```V``` 是一个数字且 ```R``` 是一个直方图。
+ ```SimpleAccumulator``` 适用于两种类型都相同的情况，例如计数器。
 
 {% top %}