The invention relates to an energy-saving hot water system for a refrigeration device in a ship's cold storage, belonging to the technical field of refrigeration and ship engineering. The invention includes a condenser, an expansion tank, a hot water stop valve, a one-way valve, a thermometer, a flow meter, a programmable controller, a replenishment valve, a circulating water pump, a return water stop valve, a seawater cooling circuit, a three-way valve, a float valve, hot water tank. According to the change of water temperature and water level in the hot water tank, through the adjustment of the programmable controller, the entire energy-saving hot water system can operate normally, and the seawater cooling circuit can ensure that the refrigeration system of the ship's cold storage is in a favorable working state and can be used to the maximum extent. The waste heat discharged from the refrigeration device makes domestic hot water use no additional energy consumption at all, which reduces the energy consumption and emission level of the whole ship. It is a waste heat utilization system that can operate stably for a long time and has reliable performance, and has significant economic benefits. and social benefits.