The invention relates to an underwater well repair assembly. The underwater well repair assembly comprises a safety joint, a blowout control valve, a totally-closed shear blade blowout preventer, a stress joint and a tie-back device which are sequentially connected from top to bottom, as well as a guiding short circuit arranged in the stress joint, wherein the safety joint is used for being connected with a drill pipe; and the tie-back device is used for being connected with an underwater Christmas tree. According to the underwater well repair assembly, well repair operation of a deep water oil and gas field can be performed by adoption of an active-service engineering ship, and a large-scale floating-type drilling platform or a special well repair ship for building is not required to be used, so that the operation cost can be greatly lowered, and the well repair efficiency is improved. As the safety joint is arranged, in case of such severe working conditions as typhoon during operation, emergency disposal can be performed, temporary well abandoning can be quickly and reliably conducted, the engineering ship or the drilling platform is withdrawn, and the safety risks during operation can be reduced. The underwater well repair assembly can be used for the engineering ship or the drilling platform, and can be widely applied to well repair operation of the deep water oil and gas field adopting an underwater production system development mode.