This article takes S7-300 series PLC as the controller and belt conveyor as the control object.And the belt conveyor is fuzzy controlled by the frequency converter.It takes the Kingview as the monitor software.It designs a belt fuzzy frequency modulation and Speed control system,which can adjust the speed rate according to different situations for belt conveyor.The results show that this system can achieve precise control to motor speed.It is practical,and has some promotional value.