The magnetic coupler is one of the important components of wireless charging system, and its coupling coefficient directly influences the energy transmission efficiency. This paper designs a magnetic coupler for Autonomous Underwater Vehicle(AUV) wireless charging in the marine environment. Firstly, the eddy current effect during energy transmission of the magnetic coupler under seawater conditions is analyzed, and the equivalent model of the wireless charging system is compensated and corrected. Then, the genetic-BP neural network algorithm is used to determine the relevant structural parameters of the magnetic coupler. Finally, the electromagnetic field simulation analysis of the offset phenomenon between the transmitting and receiving sides of the magnetic coupler is carried out based on ANSYS MAXEWLL software.The results show that the coupling coefficient of the magnetic coupler under normal operation is 0.87, and if there is a 10mm radial offset (or 5 ° circumferential offset), the coupling coefficient will decrease to 0.74 (or 0.78), which provides a reference basis for the subsequent offset fault-tolerant design of the AUV wireless charging system.