Abstract: For coil spacing is a key indicator to measure wireless power transfer distance, influence of coil spacing on performance of resonant wireless power transmission system was studied. A four-coil magnetically coupled resonant wireless power transmission system model and a PCB planar spiral coil model were established. The influence of the distance between source coil, transmitting coil, receiving coil and load coil on system transmission efficiency and output voltage were analyzed through Matlab simulation, and an experimental platform was built to verify the simulation results. The results show that the coil spacing has a significant effect on the transmission efficiency of the system. The load voltage output by the system presents a law of increasing first and then decreasing as the increase of spacing d23 between transmitting coil and receiving coil and the spacing d12 between the source coil and transmitting coil. Appropriate d23 and d12 can make the system output voltage reach the maximum value, and the increase of the distance d34 between the source coil and the transmitting coil makes the output voltage gradually decrease. Therefore, the receiving coil and load coil should be as close as possible in the system design.