Abstract: Application structure classes contained within VC++ Class Libraries MFC are all derived from base class C Object, and have many common interfaces and methods, which provides many conveniences.According to that characteristic of class, we can also build some new applicationclasses which are derived from some classes in MFC Lib, and are more efficient, more practicable, more useful and have no influence on the function modules of base classes.In this article, we expatiate and discuss on the derive method of MFC by taking for examples class C File and some class written by us.