This paper studied how to achieve hybrid electric vehicle's electric mode and engine mode switching smoothly. The main principle is the same driving torque. This paper proposed a new algorithm for the motor torque to achieve it. According to velocity and throttle and CVT's ratio, this algorithm obtains engine pseudo-target speed. According to engine output characteristics and throttle opening and engine speed，we got the engine output torque. And then we derived the motor output torque. Simulation results have shown that before and after mode switching, the vehicle drive torque is basically the same. It has been proved that the algorithm can achieve the smoothness of mode switching.