Abstract: To improve the control effect of variable air volume system, the fuzzy PID control system of supply air temperature, return air temperature and fresh air is designed comprehensively. The supply air temperature is controlled through adjusting the valve opening of chilled water. The indoor temperature is controlled by adjusting the rotational speed of variable frequency ventilator. The fresh air volume is controlled through adjusting the valve opening of fresh air. The return air volume is controlled through adjusting the valve opening of return air. The supply air temperature, the indoor temperature (return air temperature) and indoor concentration of carbon dioxide are controlled online by fuzzy PID controller. The result shows that the designed fuzzy PID controller is reasonable with good control effect.