diff --git a/include/tvm/auto_scheduler/cost_model.h b/include/tvm/auto_scheduler/cost_model.h
index 4a22b4708fded..856c907695eff 100644
--- a/include/tvm/auto_scheduler/cost_model.h
+++ b/include/tvm/auto_scheduler/cost_model.h
@@ -42,7 +42,7 @@ using runtime::TypedPackedFunc;
 class CostModelNode : public Object {
  public:
   /*!
-   * \brief Update the cost model according to new measurement pairs (training data).
+   * \brief Update the cost model according to new measurement results (training data).
    * \param inputs The measure inputs
    * \param results The measure results
    */
@@ -50,7 +50,7 @@ class CostModelNode : public Object {
 
   /*!
    * \brief Predict the scores of states
-   * \param task The search task
+   * \param task The search task of states
    * \param states The input states
    * \param scores The predicted scores for all states
    */
diff --git a/python/tvm/auto_scheduler/cost_model/cost_model.py b/python/tvm/auto_scheduler/cost_model/cost_model.py
index 9a366fab51b1d..bb9af255fc2c2 100644
--- a/python/tvm/auto_scheduler/cost_model/cost_model.py
+++ b/python/tvm/auto_scheduler/cost_model/cost_model.py
@@ -28,18 +28,40 @@
 class CostModel(Object):
     """The base class for cost model"""
 
+@tvm._ffi.register_object("auto_scheduler.RandomModel")
+class RandomModel(CostModel):
+    """A model returns random estimation for all inputs"""
+    def __init__(self):
+        self.__init_handle_by_constructor__(_ffi_api.RandomModel)
+
     def update(self, inputs, results):
+        """Update the cost model according to new measurement results (training data).
+
+        Parameters
+        ----------
+        inputs : List[MeasureInput]
+            The measurement inputs
+        results : List[MeasureResult]
+            The measurement results
+        """
         _ffi_api.CostModelUpdate(self, inputs, results)
 
     def predict(self, search_task, states):
-        return _ffi_api.CostModelPredict(self, search_task, states)
+        """Predict the scores of states
 
+        Parameters
+        ----------
+        search_task : SearchTask
+            The search task of states
+        statse : List[State]
+            The input states
 
-@tvm._ffi.register_object("auto_scheduler.RandomModel")
-class RandomModel(CostModel):
-    """A model returns random estimation for all inputs"""
-    def __init__(self):
-        self.__init_handle_by_constructor__(_ffi_api.RandomModel)
+        Returns
+        -------
+        scores: List[float]
+            The predicted scores for all states
+        """
+        return [x.value for x in _ffi_api.CostModelPredict(self, search_task, states)]
 
 
 @tvm._ffi.register_func("auto_scheduler.cost_model.random_number")
@@ -74,10 +96,47 @@ def predict_stage_func(task, states, return_ptr):
                                             predict_func, predict_stage_func)
 
     def update(self, inputs, results):
+        """Update the cost model according to new measurement results (training data).
+
+        Parameters
+        ----------
+        inputs : List[MeasureInput]
+            The measurement inputs
+        results : List[MeasureResult]
+            The measurement results
+        """
         raise NotImplementedError
 
     def predict(self, task, states):
+        """Predict the scores of states
+
+        Parameters
+        ----------
+        search_task : SearchTask
+            The search task of states
+        statse : List[State]
+            The input states
+
+        Returns
+        -------
+        scores: List[float]
+            The predicted scores for all states
+        """
         raise NotImplementedError
 
     def predict_stages(self, task, states):
+        """Predict the scores of states
+
+        Parameters
+        ----------
+        search_task : SearchTask
+            The search task of states
+        statse : List[State]
+            The input states
+
+        Returns
+        -------
+        scores: List[float]
+            The predicted scores for all stages in all states in packed format
+        """
         raise NotImplementedError
diff --git a/tests/python/unittest/test_auto_scheduler_cost_model.py b/tests/python/unittest/test_auto_scheduler_cost_model.py
index e45537b18fbaa..baad4bb03765e 100644
--- a/tests/python/unittest/test_auto_scheduler_cost_model.py
+++ b/tests/python/unittest/test_auto_scheduler_cost_model.py
@@ -15,7 +15,7 @@
 # specific language governing permissions and limitations
 # under the License.
 
-"""Test cost model"""
+"""Test cost models"""
 
 import tvm
 from tvm import auto_scheduler