diff --git a/simcse/tool.py b/simcse/tool.py
index 12b9a098..773dbeea 100644
--- a/simcse/tool.py
+++ b/simcse/tool.py
@@ -176,6 +176,31 @@ def build_index(self, sentences_or_file_path: Union[str, List[str]],
             self.is_faiss_index = False
         self.index["index"] = index
         logger.info("Finished")
+
+    def add_to_index(self, sentences_or_file_path: Union[str, List[str]],
+                        device: str = None,
+                        batch_size: int = 64):
+        
+        # if the input sentence is a string, we assume it's the path of file that stores various sentences
+        if isinstance(sentences_or_file_path, str):
+            sentences = []
+            with open(sentences_or_file_path, "r") as f:
+                logging.info("Loading sentences from %s ..." % (sentences_or_file_path))
+                for line in tqdm(f):
+                    sentences.append(line.rstrip())
+            sentences_or_file_path = sentences
+        
+        logger.info("Encoding embeddings for sentences...")
+        embeddings = self.encode(sentences_or_file_path, device=device, batch_size=batch_size, normalize_to_unit=True, return_numpy=True)
+        
+        if self.is_faiss_index:
+            self.index["index"].add(embeddings.astype(np.float32))
+        else:
+            self.index["index"] = np.concatenate((self.index["index"], embeddings))
+        self.index["sentences"] += sentences_or_file_path
+        logger.info("Finished")
+
+
     
     def search(self, queries: Union[str, List[str]], 
                 device: str = None,