Negative pressure automatic drainage device

The invention discloses a negative-pressure automatic drainage device. The negative-pressure automatic drainage device comprises a drainage pipe connected with a slag discharge opening of a blowout prevention box. A control assembly is arranged at the lower part of the drainage tee joint, and the control assembly is used for controlling the communication state of the drainage pipe; the control assembly is communicated with the blowout prevention box body through a high-pressure pipe. According to the automatic drainage device, the control assembly controlled through pressure is arranged on the lower portion of the drainage tee joint, the nylon piston is used for controlling the position of the solid rubber ball of the vibrating screen through pressure change so as to control opening and closing of the drainage pipe, response is timely, automatic control is achieved, and it is guaranteed that gas cannot leak from the drainage port.