The heat storage tank is an important part of the split solar heater. The split solar water heater consists of flat plate collector heat storage tank, auxiliary heating system, intelligent control system, pipeline and circulation system. The flat plate collector receives solar radiation and converts the collected solar radiation energy into heat energy, gradually heating the vacuum tube and the water in the collector; When the water temperature in the collector reaches the set temperature, through the temperature sensor, temperature controller, solenoid valve, water pump and other equipment, the hot water in the collector is transferred to the heat storage tank with insulation function for storage, and at the same time, the cold water is automatically replenished. When the water level reaches the upper limit of the heat storage tank, the temperature controller starts the corresponding equipment and automatically changes the operation mode of the system to a constant temperature cycle, so that the circulation between the collector and the water tank can be formed and the solar radiation energy can be used to further improve the water temperature of the water tank.