In this paper, a primary-side control strategy of WPT system based on load identification and state observer is proposed to realize CV/CC charging of batteries. The method of sampling the phase information of the primary side is proposed to realize the load identification, which has the advantage of being free from the low frequency disturbance of the voltage. In addition, a method of estimating the output current using the state observer is proposed. The appropriate feedback matrix coefficient is selected through the characteristic polynomial of the error equation, which has the advantages of high observation accuracy, good real-time performance and strong anti-interference ability. The proposed principle is simulated and verified, and the results show that the control of the closed-loop control of the primary side and the open-loop control of the receiving side can be realized, and the constant current and constant voltage charging of the sudden load can be realized.