Based on the mutual inductance model, this paper introduces two controlled voltage source from the point of electromagnetic field. The mutual inductance voltage of primary coil is the integrating of the electric field intensity which is generated by current in the secondary coil along the primary coil path, and vice versa. In order to optimize the parameters of wireless power system, the power distribution model is proposed according to the power transmission. The input power is consumed by three parts: the power lost in the primary coil resistance, the power lost in the secondary coil resistance, and the power consumed by load. The experimental results verify the power distribution model.