In the wireless energy transmission system, the loss caused by the magnetic coupling system is one of the main components of the system loss, which is related to the loss on the receiving coil, the transmitting coil and the core loss. The traditional plane spiral coil is selected and the basic parameters of the coil and magnetic core are designed, including the design of the inner and outer radius of the coil, wire type, number of turns and turn spacing, as well as the inner and outer radius, thickness and distribution of the magnetic core. The calculation of AC resistance at high frequency and the influence of various parameters on the coupling coefficient are analyzed. Smaller AC resistance and better coupling coefficient are obtained in different occasions, which can reduce the system loss and improve the overall efficiency.