Abstract: For problem that transmission efficiency of traditional magnetic coupling resonant wireless power transmission system based on single coil structure was limited by transmission distance, a magnetic coupling resonant wireless power transmission system based on variable coil structure was designed. An equivalent circuit model of the system was built, relationship between transmission efficiency and transmission distance were analyzed when the system adopted two-coil and four-coil respectively, and conclusions were gotten as follows: transmission efficiency of the system with two-coil structure decreased with increase of transmission distance, and transmission efficiency of the system with four-coil structure increased first and then decreased with increase of transmission distance. According to above conclusions, a coupling resonant mode using variable coil structure was proposed, which adopted two-coil structure when transmission distance was smaller than coil radius and four-coil structure when transmission distance was larger than coil radius, so as to realize the maximization of transmission efficiency under different transmission distances. The simulation and experimental results verify effectiveness and validity of the system.