The invention discloses a stainless-steel U-shaped body for an expansion joint and an application method thereof, and relates to a waterproof structure. The problem that through an existing water stopping belt, after an installing groove is deformed, water easily flows into an expansion joint from a gap between the water stopping belt and the installing groove is solved. According to the technicalscheme, the stainless-steel U-shaped body for the expansion joint comprises a bottom plate, an air sac, a connecting plate arranged at the top of the air sac, a connecting pipe communicated with theair sac and a pressure meter arranged on the connecting pipe and used for measuring air pressure in the connecting pipe and the air sac; the bottom plate comprises a U-shaped plate which is located inthe expansion joint and has an opening formed upwards and an installing plate which is fixedly connected to the two sides of the top of the U-shaped plate and extends into the installing groove of awall; the connecting plate comprises a U-shaped part located at the top of the U-shaped plate and an installing part which is fixedly connected on the two sides of the top of the U-shaped part, extends into the installing groove of the wall, and is parallel to the installing plate, the connecting plate can be expanded shrunk along with shaped changes of the installing groove, and good fitting between the connecting plate and the installing groove invariably exists.