diff --git a/components/drivers/src/completion.c b/components/drivers/src/completion.c
index b91ae3d6dc..f13718f9b3 100644
--- a/components/drivers/src/completion.c
+++ b/components/drivers/src/completion.c
@@ -6,6 +6,7 @@
  * Change Logs:
  * Date           Author       Notes
  * 2012-09-30     Bernard      first version.
+ * 2021-08-18     chenyingchun add comments
  */
 
 #include <rthw.h>
@@ -15,6 +16,11 @@
 #define RT_COMPLETED    1
 #define RT_UNCOMPLETED  0
 
+/**
+ * @brief This function will initialize a completion object.
+ *
+ * @param completion is a pointer to a completion object.
+ */
 void rt_completion_init(struct rt_completion *completion)
 {
     rt_base_t level;
@@ -27,6 +33,22 @@ void rt_completion_init(struct rt_completion *completion)
 }
 RTM_EXPORT(rt_completion_init);
 
+/**
+ * @brief This function will wait for a completion, if the completion is unavailable, the thread shall wait for
+ *        the completion up to a specified time.
+ *
+ * @param completion is a pointer to a completion object.
+ *
+ * @param timeout is a timeout period (unit: OS ticks). If the completion is unavailable, the thread will wait for
+ *                the completion done up to the amount of time specified by the argument.
+ *                NOTE: Generally, we use the macro RT_WAITING_FOREVER to set this parameter, which means that when the
+ *                completion is unavailable, the thread will be waitting forever.
+ *
+ * @return Return the operation status. ONLY when the return value is RT_EOK, the operation is successful.
+ *         If the return value is any other values, it means that the completion wait failed.
+ *
+ * @warning This function can ONLY be called in the thread context. It MUST NOT be called in interrupt context.
+ */
 rt_err_t rt_completion_wait(struct rt_completion *completion,
                             rt_int32_t            timeout)
 {
@@ -94,6 +116,11 @@ __exit:
 }
 RTM_EXPORT(rt_completion_wait);
 
+/**
+ * @brief This function indicates a completion has done.
+ *
+ * @param completion is a pointer to a completion object.
+ */
 void rt_completion_done(struct rt_completion *completion)
 {
     rt_base_t level;