The invention relates to a water-saving closestool water tank. Two water outlets are formed in a water tank and are connected through a three-way pipe; a height difference is present between the two water outlets; an independent control switch is arranged on each of the two water outlets respectively; the three-way pipe is a plastic three-way pipe; the two independent control switches are arranged on two sides of the top of the water tank respectively; and the height difference between the two water outlets is 1/2 of the total height. According to flushing quantity of a urinal, a water outlet and a switch are additionally arranged in the conventional water tank, a three-way pipe is additionally arranged in the middle of the two water outlets, and a height difference is present between the two water outlets, so that urine can be just flushed through water outlet quantity at a water outlet, the problem that the conventional water-saving water tank used in public places is high in cost is solved, and the water tank is simple, low in price, high in cost performance and convenient to control. Compared with the traditional flush toilet, the water-saving closestool water tank has the characteristics of high cost performance and water resource saving.