Water stopping device and water stopping method for underground concrete diaphragm wall

The invention discloses a water stopping device and a water stopping method for an underground concrete diaphragm wall, and belongs to the field of seepage prevention of the underground concrete diaphragm wall. The water stopping device comprises a steel plate A, a steel plate B and a rubber water stopping belt, and the steel plate B comprises a first section plate part, a second section plate part and a third section plate part; the first-section plate part, the second-section plate part and the third-section plate part are sequentially connected and are integrally in a [shape, the steel plate B is arranged on the outer side of the steel plate A in a sleeving mode, and a cavity is defined by the steel plate B and the steel plate A; the rubber waterstop is arranged on the steel plate A in a penetrating manner, and one part of the rubber waterstop extends into the cavity and is in an elastic deformation state; and after the steel plate B is lifted away from the steel plate A, the rubber waterstop can extend ou