This paper investigates the underwater capacitive wireless power transfer technology for the electric ship charging application. The theoretical coupling model of the underwater capacitive coupler is proposed, and the typical structure of the charging system is then provided, based on which the power transfer capability of an underwater system is derived. A design example is provided to illustrate the proposed system in the fresh water environment. The finite element (FEM) analysis by HFSS shows that the underwater coupler is able to provide the high power capability up to MW level, which is sufficient to charge the electric ship rapidly. In the laboratory environment, in order to validate the proposed underwater capacitive power transfer system, a downsized long-distance and low-power prototype is designed and implemented. The plate size is 200mm×200mm. The experimental results have achieved hundreds of Watt power transfer over a distance of 500mm.