Submarine communication optical cable is the main carrier of international communication, and the accelerated growth of international internet bandwidth has promoted the accelerated construction of submarine communication optical cable. This paper introduces the basic structure of the power supply system for submarine communication optical cable underwater equipment, analyzes the working principles and internal circuit design of submarine repeaters, submarine branch unit, and power supply equipment. This paper proposes the design method of power supply system design for submarine communication optical cable underwater equipment, and analysis the switching protection mechanism of the power supply system combined with a case.