The invention relates to an automatic cleansing fluid release water tank. The automatic cleansing fluid release water tank comprises a cleansing fluid box filled with cleansing fluid and a flushing water tank, wherein the flushing water tank comprises a tank body; a water piece, a water overflow pipe, a flushing valve component, a fluid suction device, a fluid suction check valve, a fluid outlet check valve and a water and fluid mixing joint are arranged in the tank body; a sealed fluid suction cavity and a sealed water pressure cavity are formed in the fluid suction device; the fluid suction cavity is isolated from the water pressure cavity through an elastic membrane; and a reset mechanism of the elastic membrane is arranged in the fluid suction device. According to the water tank, the fluid suction device in which the volume of the fluid suction cavity is changed by using water pressure as power to suck and extrude liquid soap is provided, moving parts are not provided, and abrading and blocking conditions are prevented, so that the water tank is reliably operated; and in addition, the water pressure is used as the power, so that a power supply, a battery and the like are not needed, the problems of complicated control over a circuit or low environment friendliness of the battery are solved, the danger of electricity is eliminated, and the like.