Abstract: Provided is a leakage monitoring device for a pneumatic drain valve of a steam turbine. The disclosure relates to the technical field of leakage monitoring of drain valve. The device includes an additional valve body, a top flange of the additional valve body is provided with an additional sealing cover, a bucket is installed in a middle of an inner side of the additional valve body, an upper part of a left side of an outer surface of the additional valve body is fixedly connected with a water inlet pipe, a first guide cavity is vertically arranged on the inner side of the additional valve body and close to the water inlet pipe and is communicated with the water inlet pipe.