The utility model discloses an automatic sewage drainage device. The automatic sewage drainage device comprises a water seal tank, a through pipe, an overflow pipe, a sewage inlet pipe and a sewage clearing port, wherein the water seal tank is a sealed tank body; the through pipe is arranged at the top of the tank body and communicated with the atmosphere; the overflow pipe is arranged on the side wall of the tank body; the sewage inlet pipe is inserted into the tank body from the top of the tank body, and the bottom of the sewage inlet pipe is lower than the position of the overflow pipe; and the sewage clearing port is formed at the lower part of the side wall of the tank body, and a valve is arranged on the sewage clearing port. According to the pressure difference theory, the gas in a high-temperature furnace gas pipeline is sealed by using the liquid in the water seal tank; and gas seal with the liquid and automatic drainage of the liquid are realized by means of the liquid pressure of a sewage inlet pipe and the height of the liquid level at the overflow pipe in the water seal tank.