The utility model relates to the technical field of drainage devices, in particular to a drainage valve which comprises a tubular valve body, a locking nut and a plug, one end of the tubular valve body extends outwards in the radial direction to form a baffle ring, external threads are arranged on the outer surface of the tubular valve body, and the locking nut is connected with the external threads of the tubular valve body in a matched mode. An internal thread is arranged in the end, away from the baffle ring, of the tubular valve body, an external thread is arranged outside the plug, the external thread of the plug is connected with the internal thread of the tubular valve body in a matched mode, a connecting rod is arranged at the end, away from the handheld part, of the plug, and a limiting supporting rod is arranged at the end of the connecting rod. The limiting supporting rod is used for limiting the connecting rod from being pulled out of the tubular valve body. According to the utility model, the tubular valve body and the locking nut are mounted on the box body, meanwhile, the plug is used for sealing, the plug is connected with the tubular valve body through the connecting rod and the limiting support rod, and the plug cannot be completely separated from the tubular valve body in the drainage process, so that the loss cannot be caused, and the use performance is improved.