The inductively coupled mooring cable is an important tool for monitoring the ocean hydrological data. The mooring cable is an open-loop structure that uses a section of seawater as the transmission medium. The power transmission efficiency of this structure is very low due to the large power loss of the seawater medium, and it is rarely studied. In this paper, a contactless power transmission circuit with seawater loss is analyzed, and the theoretical model of multi-node power transmission of the inductively coupled mooring system is established. In this model, the improvement of the output power and transmission efficiency is only related to the frequency selection and the properties of the magnetic core itself, such as the magnetic core material. Moreover, the optimal scheme is selected according to the output power requirements. The experimental results show that when the input current (Irms) is 2A, the output power of a single node is 12W, the total output power is 120W, and the total transmission efficiency reaches 50%.