Disclosed are an instantly closed drainage device and a closestool. The instantly closed drainage device comprises a box body component and a drainage valve component, the box body component is used for storing water, the drainage valve component can be controlled to drain off water, the box body component comprises a large piston group and a pressure chamber, the drainage valve component comprises a backpressure chamber, a moving mechanism and a drainage pipe, the pressure chamber is communicated with the drainage pipe, and the moving mechanism is arranged between the pressure chamber and the backpressure chamber and can seal or open the drainage pipe. The instantly closed drainage device is characterized by further comprising a control component and a connecting channel, the connecting channel is communicated with the pressure chamber and the backpressure chamber, and the control component is disposed on the connecting channel to control opening and closing of the connecting channel. According to the instantly closed drainage device and the closestool, actions of the control component depend on movement of the large piston group, the control component can control opening and closing of the connecting channel and drive the moving mechanism to move to seal the drainage pipe, instant closing of drainage can be achieved, and relatively stable drainage amount and drainage time can be guaranteed.