This paper presents the basic idea．notation and development process of an object—oriented anMysis and design method through the development of a data flow dia-gram editor,This method takes a responsibility—driven modelling approach to software development，emphasizing that software simulates the real world．It starts with problem —understanding to build a user model of the problem，then this model is evolved into an implementation model through an iterating five—stage—process during each phase of the software development process．The five stages include：dividing subjects，identifying classes，establishing relations，defining services and defining attributes．Based cn behav-ior analysis，the user problem is first divided into a set of subjects．each of which hosts a number of classes with distinguished responsibilities and collaborators The responsibili- ties then hlrther help define the services and attribules of each class and their inter—rela-dons．All these put together give software developers a clear layered model of the pro-posed system．