The wireless power transfer system based on SN ( Series-None compensation) has the advantages of high efficiency in the case of strong coupling and high quality factor as well as simple-structured receiver． In order to deal with the unstable voltage caused by mutual inductance shifting and load fluctuation，a primary side detection method was proposed． The actual mutual inductance and output voltage of the receiving side were calculated by measuring the input voltage and current of the transmitting side and the phase difference between them． The closedloop control was realized on this basis． In this paper，the principle of the primary side detection of the system based on Series-None compensation topology and the efficiency characteristics of the system were analyzed firstly． Then the theoretical analysis was verified by the simulations of open loop and closed loop respectively with Simulink simulation software． Finally，the feasibility of the control method was verified by experiments． Simulation and experimental analysis proves that the control method proposed in the article is correct and effective．