Human exploration of the ocean is inseparable from reliable ocean observation equipment. Wireless power transmission technology can supply power to the receiving end in a non-contact manner, saving complicated cable plugging and unplugging. Due to the conductivity of seawater, a certain amount of eddy current loss will be generated during wireless power transmission, reducing the output power and transmission efficiency. This paper designs a wireless power transmission system suitable for underwater scenes, and in this paper, the operational characteristics of the system are analyzed. At the same time, the transmission capability of the system in the air is studied, and the influence of several key parameters such as resonance frequency on the output power and transmission efficiency is analyzed. On this basis, combined with the calculation method of eddy current loss in seawater, the system transmission efficiency in seawater is calculated, which provides a reference for selecting the operating frequency. Finally, a coupler design scheme that is easy to dock with underwater devices and has a good electromagnetic shielding effect is given, and its transmission capability and performance under misalignment are analyzed through finite element simulation. According to the design plan, a prototype is built and experiments are carried out in air and simulated seawater environments. The experimental results verify the correctness of the theory.