The utility model relates to the technical field of closestools, in particular to a pneumatic control closestool with a water tank hidden below a closestool, which comprises the closestool and the hidden water tank arranged at the tail of the closestool. A water inlet valve, a pneumatic button and a drain valve are arranged in the hidden water tank; the exhaust end of the pneumatic button is respectively communicated with the water inlet valve and the drain valve; a water inlet is formed in the bottom of the water inlet valve, a water flow channel is transversely formed in the water inlet valve, an air inlet is formed in the position, located at the water outlet connector, of the water inlet valve, and a positioning sleeve, a water stop pad and a water stop cover are sequentially arrangedat the air inlet from inside to outside. According to the utility model, the double-function water inlet valve and the pneumatic large-caliber drain valve are utilized; when the closestool is used, the closestool water tank can be hidden under the closestool, the sewage discharge surface of the closestool is flushed and decontaminated by utilizing the pressure of a water supply source, the bottomof the closestool is greatly flushed and decontaminated by utilizing the pneumatic large-caliber drain valve, the closestool water tank is hidden under the closestool while water is saved, and the attractiveness of the closestool is improved.