The invention discloses a joint protection plate for an underground continuous wall, a construction machine and a construction method, and relates to a construction device for protecting joints of a continuous all in hydraulic and hydro-power engineering and a construction method. The protection plate is an arc-shaped plate, and comprises a pulling plate, a standard plate and a bottom plate. The construction machine for the joint protection plate of the underground continuous wall comprises a plate pulling system, a pulling cushion frame and a top plate reinforcing device of an original reinforcement cage framework; the plate pulling system comprises a rail pin beam and plate pulling machines; the two ends of the rail pin beam are supported by the plate pulling machines respectively; the other end of one plate pulling machine is arranged on the ground, and the other end of the other plate pulling machine is arranged on the lifting cushion frame. The joint protection plate has the beneficial effects that in underground continuous wall construction, the joint protection plate is arranged in a groove-shaped steel plate joint, so that concrete is prevented from entering a groove of the steel plate joint and being bonded with the joint of the groove-shaped steel plate, a high construction speed is achieved, the labor intensity of workers is lowered, the conventional bag-throwing construction method is broken through, and a beneficial condition is created for overlapping construction of wall plates.