Base on the research of repair technology on seal welding defects of non-regenerative heat exchanger tube to tube plate in nuclear power plant,the process and technical requirements of repairing defects are introduced in this paper. The successful application of the repair welding technology of the first pass self-fluxing and the second filler wire in the repair engineering of seal welding defects of the tube to tube plate has guaranteed the welding quality,promoted the weld forming and improved the maintenance efficiency.This technology can realize the on-line repair of seal weldind defects on heat exchanger tube to tube plate and provide an important reference for the following similar work.