Compared with traditional wired charging, wireless charging is a more convenient and reliable charging method, which has a wide application prospect in some fields such as electric vehicles and bio-medicine. However, the low transmission efficiency limits the further popularization of wireless energy transmission technology. As one of the most important wireless energy transmission technologies, magnetic-coupled resonance is mainly composed of high-frequency power supply, compensation structure, magnetic coupling structure and rectifier-filter structure. At present, when analyzing the transmission efficiency of magnetic coupling resonant wireless energy transfer system, only the loss of magnetic-coupled structure is considered, but the loss of high-frequency power source and rectifier- filter structure in the system is less considered. In this paper, the relationship between losses and mutual inductance of each part of the magnetic coupling resonant wireless energy transfer system is calculated under the predetermined efficiency and constant power conditions, and the mutual inductance value satisfying the system requirements is sought. Finally, a magnetic coupling resonant wireless energy transfer system with transmission power of 1000W and transmission efficiency of 85% is designed and experimental results show that the loss calculation method is accurate. The research results of this paper play a positive role in promoting the analysis and performance improvement of wireless charging system.