To enhance the system's response speed and anti-interference capability and reduce the speed fluctuations of the range extender, a method of using generator torque to compensate for engine torque vibration is peoposed. The output torque of the engine to determine the influence of the harmonic components in the torque on the speed is analyzed. Then, a control strategy combining an adaptive backstepping method and a repetitive controller is designed. The repetitive controller is parameterized based on the fundamental frequency of the periodic torque disturbance of the system, and the stability and robustness of the system are analyzed. Finally, simulation experiments are conducted under different operating conditions, and the results show that this control strategy has good effectiveness and practicability in suppressing the speed fluctuations of the range extender.