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diff --git a/docs/user_guide.md b/docs/user_guide.md
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--- a/docs/user_guide.md
+++ b/docs/user_guide.md
@@ -30,6 +30,7 @@ This guide walks you through the fundamentals of using Harbor. You'll learn how
 * [Online Garbage Collection.](#online-garbage-collection)
 * [View build history.](#build-history)
 * [Manage robot account of a project.](#robot-account)
+* [Using API Explorer](#api-explorer)
 
 ## Role Based Access Control(RBAC)  
 
@@ -637,3 +638,15 @@ If you are a project admin, you can disable a Robot Account by clicking "Disable
 If you are a project admin, you can delete a Robot Account by clicking "Delete" in the `Robot Accounts` tab of a project.
 ![delete_robot_account](img/robotaccount/disable_delete_robot_account.png)
 
+## API Explorer
+
+Harbor integrated swagger UI from 1.8. That means all apis can be invoked through UI. Normally, user have 2 ways to navigate to API Explorer. 
+
+1. User can login harbor, and click the "API EXPLORER" button.All apis will be invoked with current user authorization.                         
+![navigation bar](img/api_explorer_btn.png)  
+
+
+2. User can navigate to swagger page by ip address by router "devcenter". For example: https://10.192.111.118/devcenter. After go to the page, need to click "authorize" button to give basic authentication to all apis. All apis will be invoked with the authorized user authorization. 
+![authentication](img/authorize.png)
+
+