In the process of wireless charging,the fluctuation of output power is caused by the change of battery resistance,which shortens the battery life and affects the safety of charging. For the magnetic coupling resonance type wireless power transmission variable load system,the control circuit is usually added at the receiving end to stabilize the output power,but it expands the volume of the electrical equipment. Therefore,two constant power control strategies based on the principle of reflected impedance are proposed in the article,namely Sepic circuit constant power output control strategy and phase shift control constant power output control strategy. Firstly,the influence of load resistance on the output power is analyzed. Secondly,the relationship between the duty cycle of the Sepic circuit drive signal and the output power,and the relationship between the phase shift angle of the drive signal and the output power in the phase shift control are deduced respectively. The principle of the constant power control strategy in the article is given. Finally,a simulation model is built through Matlab/Simulink to verify the correctness of the theoretical analysis and the proposed control strategies. The simulation results show that both control strategies can effectively achieve constant power output.