By analyzing the control line principle of hydroviscous drive,it was obtained the part of the flow rate of the hydraulic pump was backed into the tank by the throttle valve and the other part was leaked back into the tank through internal leakage.It was further established the dynamic model and the relationship between the system oil pressure and the power supply frequency,when the speed of the pump was adjusted by the frequency converter.Finally,MATLAB software was used to analyze the controllability of the hydraulic pressure of the system.