Abstract: An equivalent circuit model of three-coil magnetic coupling resonant wireless power transmission system was built, and formulas of system transmission power and transmission efficiency were deduced. Coupling factors relation with the maximum system transmission power was obtained under critical coupling state, and relationship expression between coupling factor and frequency splitting point was given. Frequency characteristics of the system were analyzed. The theoretical analysis results show that there is frequency splitting phenomenon in the system under overcoupling state with three frequency splitting points; the system only resonates at inherent resonant frequency under critical coupling state and undercoupling state; whether there is frequency splitting phenomenon or not, the system resonates at inherent resonant frequency, and transmission power of the system reaches the maximum. The simulation and experimental results verify correctness of the theoretical analysis.