In view of a reduction of the influence of load torque disturbance on the control of permanent magnet synchronous motors, an improved load torque observer has thus been designed. The load torque observer is established with the speed and load torque as the observation object, the observed load torque is fed forward and compensated to the torque current, with the variable gain algorithm added to suppress the chattering problem of the output of the sliding mode speed controller. The improved sliding mode speed controller is used to replace the traditional PI control, and meanwhile the system response speed is improved by improving the exponential reaching law function in the controller. Simulation results show that the method can accurately observe the load torque, and reduce the chattering problems, thus improving the anti-interference ability and dynamic response performance of the system.