For the wireless charging of electric vehicles, considering the radial offset of transmitting coil and receiving coil, based on the series topology of two coil structures, the anti-offset performances of circular, rectangular and DD coils are compared by 3D electromagnetic simulation software Maxwell. The selected coil is optimized by adding magnetic core and aluminum plate. Joint simulation is realized with the help of Maxwell and Simplorer to verify the feasibility of the design of the wireless power transmission system. In the case of offset between the two coils, to achieve the transmission efficiency of the wireless power transmission system of 95% and above, a design process of magnetic coupling mechanism based on coil comparison and selection is given, and a practical wireless power transmission system is designed according to the process. Finally, its feasibility is verified through experiments