Based on the analysis of expert experience on generation system planning(GPS), the theory of knowledge based method is introduced into GPS to express the constraints of engineering(viz. Expert experience of engineering), and to discard abundant improper program during the earlier stage of GPS. In this situation, the difficulty degree of optimizing calculation in the later stage of GPS is lessened. And then, integrating expert system with production simulation in a method of GPS is proposed and is verified with an example. The results show that the method presented is effective.