Underground sewage draining system

The utility model relates to an underground sewage draining system. The underground sewage draining system comprises a foundation, wherein a deposition pipe is arranged in the foundation; the left end of the deposition pipe is connected with a water supply upright pipe; the water supply upright pipe is connected with a water supply pipe; the right end of the deposition pipe is respectively connected with a drainage upright pipe and a sewage drainage pipe through a tee; the drainage upright pipe is connected with a drainage pipe; the other end of the sewage drainage pipe is connected with a sewage drainage unit; the water supply upright pipe, the deposition pipe and the drainage upright pipe form a U-shaped sewage draining structure. The problem that an engineering process is affected because a U-shaped pipe is not easily dredged after being blocked in the prior art is solved, and the underground sewage draining system has very high application value.