The invention discloses an in-service nuclear power station main equipment safety end weld defect repairing method. The method comprises the following steps that 1, multi-weld-pass multi-layer weldingis applied to the low-alloy steel side of a stainless steel main pipeline and a low alloy steel main device which are in welded connection from exterior to interior; 2, water is led into the stainless steel main pipeline, and multi-layer bead welding is applied to all positions; 3, whole bead welding of follow-up weld passes is performed on the bead welded priming layer from low-alloy steel sideto the stainless steel side. Compared with the prior art, the in-service nuclear power station main equipment safety end weld defect repairing method has the advantages that multiple layers of stresscorrosion resisting materials are welded to the outer wall of a pipeline with defects on the inner wall, so that the strength of the pipeline with the defects is improved; meanwhile, compression stress is generated on the inner wall of the pipeline, so that the defects are prevented from being further expanded, the repairing method is simple and rapid, the whole pipeline with overproof defects atthe safety end welding bead does not need to be replaced, and the safety operation of a nuclear power station can be ensured.