Abstract: The hot air system adopting simple PID control in primary processing line cannot adapt to the requirements of different processing technologies,therefore the control system was improved with fuzzy control algorithm.A fuzzy controller for hot air temperature was designed by adopting PLC of series S7-400,the input and output variables of fuzzy controller were determined coupling with measuring range switching.The values for each variable in fuzzy language and relevant membership functions were also determined.The rules of fuzzy control were established,and the hot air temperature system was controlled according to the requirements of the PID parameters of fuzzy control system.The results of application showed that:the fuzzy control system featured fast startup,steady temperature output,minor over regulation.The temperature of hot air could be controlled within setting value±0.5℃.When the setting value of hot air temperature was changed,the control system responded quickly and steadily,the stability and control precision of hot air control system were improved.