In the traditional power grid frequency control system, PI control is often adopted to adjust the frequency, while it causes some problems such as long settling time and over-shoot, so the fuzzy control theory is introduced. Taking conventional generator as the research object, to improve frequency regulatory performance, a composite structure controller of the fuzzy PID is designed which can adjust the parameters of the PID controller by itself according to the range of the frequency offset. The models of water and fire units are built in Simulink and fuzzy PID controller is joined to improve the system frequency regulation and make simulations. The result of the simulations and data analysis verify the feasibility of the plan, compared with the traditional frequency control, the fuzzy PID controller can improve the dynamic response and reduce error of the system. This work is supported by National Natural Science Foundation of China (No. 61304177) and Scientific Research of Sichuan Education Department (No. 15ZB0345).