diff --git a/.github/workflows/persubmit.yml b/.github/workflows/persubmit.yml
index 244383cff9807..51b2cbad4c3da 100644
--- a/.github/workflows/persubmit.yml
+++ b/.github/workflows/persubmit.yml
@@ -57,6 +57,21 @@ jobs:
           ti diagnose
           ti test -vr2 -t2
 
+  check_previous_run:
+    name: Checks the Workflow Run of the Previous Commit
+    runs-on: ubuntu-latest
+    if: ${{ contains(github.event.pull_request.labels.*.name, 'skip ci') || github.event.sender.login == 'taichi-gardener' }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+      - name: Check the previous run
+        run: |
+          PR=${{ github.event.pull_request.number }}
+          SHA=${{ github.event.pull_request.head.sha }}
+          python misc/ci_check_previous_run.py --pr ${PR} --sha ${SHA}
+
   code_format:
     name: Code Format
     runs-on: ubuntu-latest
diff --git a/misc/ci_check_previous_run.py b/misc/ci_check_previous_run.py
new file mode 100644
index 0000000000000..7b4a8cb1a5b99
--- /dev/null
+++ b/misc/ci_check_previous_run.py
@@ -0,0 +1,133 @@
+import argparse
+import json
+import logging
+import time
+import urllib.request as ur
+import sys
+
+API_PREFIX = 'https://api.github.com/repos/taichi-dev/taichi'
+SHA = 'sha'
+
+
+def make_api_url(p):
+    return f'{API_PREFIX}/{p}'
+
+
+def send_request(url):
+    logging.debug(f'request={url}')
+    return ur.urlopen(url)
+
+
+def get_commits(pr):
+    url = make_api_url(f'pulls/{pr}/commits')
+    f = send_request(url)
+    return json.loads(f.read())
+
+
+def locate_previous_commit_sha(commits, head_sha):
+    """
+    Returns the previous commit of |head_sha| in PR's |commits|.
+    """
+    assert commits[-1][SHA] == head_sha
+    if len(commits) < 2:
+        return None
+    return commits[-2][SHA]
+
+
+def get_workflow_runs(page_id):
+    # https://docs.github.com/en/rest/reference/actions#list-workflow-runs-for-a-repository
+    url = make_api_url(f'actions/runs?page={page_id}')
+    f = send_request(url)
+    return json.loads(f.read())
+
+
+def is_desired_workflow(run_json):
+    """
+    Checks if this run is for the "Presubmit Checks" workflow.
+    """
+    # Each workflow has a fixed ID.
+    # For the "Persubmit Checks" workflow, it is:
+    # https://api.github.com/repos/taichi-dev/taichi/actions/workflows/1291024
+    DESIRED_ID = 1291024
+    return run_json['workflow_id'] == DESIRED_ID
+
+
+def locate_workflow_run_id(sha):
+    done = False
+    page_id = 0
+    while not done:
+        # Note that the REST API to get runs paginates the results.
+        runs = get_workflow_runs(page_id)['workflow_runs']
+        for r in runs:
+            if r['head_sha'] == sha and is_desired_workflow(r):
+                return r['id']
+        page_id += 1
+    return ''
+
+
+def get_status_of_run(run_id):
+    """
+    Waits for run identified by |run_id| to complete and returns its status.
+    """
+    url = make_api_url(f'actions/runs/{run_id}')
+    start = time.time()
+    retries = 0
+    MAX_TIMEOUT = 60 * 60  # 1 hour
+    while True:
+        f = send_request(url)
+        j = json.loads(f.read())
+        # https://developer.github.com/v3/checks/runs/#create-a-check-run
+        if j['status'] == 'completed':
+            c = j['conclusion']
+            logging.debug(f'run={run_id} conclusion={c}')
+            return c == 'success'
+
+        if time.time() - start > MAX_TIMEOUT:
+            return False
+        retries += 1
+        logging.info(
+            f'Waiting to get the status of run={run_id} (url={url}). retries={retries}'
+        )
+        time.sleep(15)
+    return False
+
+
+def get_cmd_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--pr', help='PR number')
+    parser.add_argument('--sha', help='Head commit SHA in the PR')
+    return parser.parse_args()
+
+
+def main():
+    logging.basicConfig(format='%(asctime)s %(levelname)s:%(message)s',
+                        level=logging.DEBUG,
+                        datefmt='%Y-%m-%d %H:%M:%S')
+    args = get_cmd_args()
+
+    pr = args.pr
+    commits = get_commits(pr)
+    num_commits = len(commits)
+    logging.debug(f'\nPR={pr} #commits={num_commits}')
+
+    head_sha = args.sha
+    prev_sha = locate_previous_commit_sha(commits, head_sha)
+    logging.debug(f'SHA: head={head_sha} prev={prev_sha}')
+    if prev_sha is None:
+        logging.info(f'First commit in PR={pr}, no previous run to check')
+        # First commit in the PR
+        return 0
+
+    run_id = locate_workflow_run_id(prev_sha)
+    if not run_id:
+        logging.warning(f'Could not find the workflow run for SHA={prev_sha}')
+        return 0
+
+    logging.info(f'Prev commit: SHA={prev_sha} workflow_run_id={run_id}')
+    run_ok = get_status_of_run(run_id)
+    logging.info(f'workflow_run_id={run_id} ok={run_ok}')
+    return 0 if run_ok else 1
+
+
+if __name__ == '__main__':
+    sys.exit(main())