In large-area HFCVD system, substrate temperature is a key factor which deeply affects the quality of diamond films. It is hard for traditional PID method to control the temperature efficiently. This paper presents a genetic- based PID control scheme for the control of in HFCVD system. Computer simulation and experiment on the system are performed. The results show that the controller designed upon GAs has good dynamic quality and steady-state precision, could meet well the need of the temperature control during depositing diamond films.