Visual programming environment has brought about great changes in the development of human-machine interface. It enables the developers to implement human-machine interface using visual operations by means of what you see is what you get, and the program code can be generated automatically by the environment. This change gives rise to some new problems to object-oriented design of human-machine interface. Since the implementation of the interface does not depend on manual programming, is it necessary to design before implementation? And what is the use of the class diagram built at the design stage? The answers to these questions can be found in this paper. It proves that the design is necessary yet in that environment, but its strategies s...