This paper suggests a implements and a design of class diagram authorization tool based on the MVC pattern. It defines and descries the structure of ClassInformation, ScreenDisplay and ToolManager. ClassInformation is responsible for processing or handling information of a diagram. ScreenDisplay is responsible for GUI to configure the screen of the authorization tool. ToolManager is responsible for event handling to process I/O of the authorization tool. Based on MVC pattern, ClassInformation, ScreenDisplay and ToolManager of the authorization tool are assigned each role independently. It is flexible to new requirement, because of loose coupling.