Subway tunnel leaking stoppage and pressure relief device

The utility model provides a subway tunnel leaking stoppage and pressure relief device which comprises an injection cylinder, a plurality of injection holes are formed in the outer side of the injection cylinder, the injection holes are arranged at equal intervals, the upper side of the injection cylinder is fixed to a connecting pipe, the upper side of the connecting pipe is fixed to a threaded connecting cylinder, and the threaded connecting cylinder is connected with the injection cylinder. The threaded connecting cylinder is connected with a conveying pipe through a screw opening, the outer side of the injection cylinder is sleeved with an expansion air bag, the outer side of the expansion air bag is provided with an outer limiting structure, the outer limiting structure is attached to the hole wall of the interior of the water leakage hole, and the interior of the air bag body is inflated through an inflation device via an inflation valve opening; the outer wall of the air bag body is attached to the hol