As the Information Age coming, more and more factories take the advantages of automation control. Therefor, the Human-Machine Interface(HMI) System are getting more and more important. So, building a HMI System with high flexibility and low cost has become an important point. This research is focused on the flexibility of HMI program. We use a new structure of program, add a common interface between each level to make each level more independent. And we take the conception of ¡§Design Patterns¡¨ of GOF to make each module more flexible. Then, we design a new way for the module communication.