According to the requirement of stable temperature control of heat sealing cutting knife in pantyhose packaging bag-making process, the influencing factors of heat sealing cutting knife temperature were analyzed and its simplified model was established. The control system based on PIC16F877 was designed, and the algorithm of controller was fuzzy-PID. Temperature control was realized through control the closed time of SSR. The results of MATLAB simulation showed that fuzzy-PID controller can cut down the overshoot and reduce the setting time; this system has good dynamic characteristic.