A speed sliding mode control method based on load torque observer is proposed to solve the problem of poor speed regulation performance of brushless DC motor (BLDC) due to frequent load changes. The sliding mode variable structure control method is used in the speed loop, and the speed sliding mode controller is designed based on the improved exponential reaching law. At the same time, in order to reduce the impact of load torque disturbance on the motor operation state, a load torque observer is designed based on the Luenberger observer, which estimates the actual load torque and feed-forward the output of the observer to the speed sliding mode controller to counteract the impact of load torque disturbance. In order to verify the effectiveness of the proposed scheme, a simulation model is built and analyzed in MATLAB/Simulink simulation environment. The simulation results show that the brushless DC motor system based on load torque observer and speed sliding mode controller has excellent performance. Compared with traditional PI control, the proposed scheme has strong anti-interference ability, short recovery time, and fast speed response. The effectiveness of the proposed scheme is proved.