The invention relates to an overflow alarm automatic closing device after water is supplied to a solar water heater, in particular to a solar water heater overflow automatic closing device. When water is supplied to an existing solar water heater, a person is often needed for watching the solar water heater and closing a water valve after the solar water heater is filled with the water; sometimes, tap water is wasted due to negligence. In order to overcome the defect, a thin film water vat is connected to a water supply pipe, a micropore overflow valve is connected to a water return pipe, different speeds of air ventilation and water flow in micropores in the micropore overflow valve are utilized for triggering the thin film water vat to pull a trigger and drive an actuating device, a four-bar mechanism is driven to close the water valve, and therefore the purposes of unattended operation and water conservation are achieved.