Compared with the three-coil relay wireless power transmission structure, the two-coil structure has higher efficiency but short distances, while the three-coil structure is mostly used for medium and long-distance wireless power transmission, the efficiency is low in the short-distance system. For electric vehicles with different chassis distances, resulting in low charging efficiency, a U-shaped coil switching system based on vertical relay is presented here. The system switches at a suitable distance point, that is, the optimal efficiency can be reached at different transmission distance, the problem of low efficiency caused by changes in spacing is solved. This paper has analyzed the three-coil circuit model, its coil characteristics, load characteristics and energy transmission distance characteristics are analyzed and optimized, efficiency influence factors have been deduced, and system simulation analysis are performed. The simulation results show that compared with the single two-coil or three-coil structure model, the designed switching system improves the wireless power transfer efficiency by 58% at both near and far distances compared with the two-coil structure, and compared with ordinary three-coil structure, the system has increased to its highest efficiency of 71%.