Abstract: Refuelling tank floor leakage has become a common problem in nuclear power plants. This paper first introduces the leakage background and structure of refuelling tank in nuclear power plant, and expounds the leakage causes, common leakage forms and common leak detection methods; In order to solve the problem that leakage points cannot be accurately and comprehensively investigated at present, three improved and optimized leak detection methods are proposed, including: new leakage detection technology of reverse osmosis method, proposed vacuum box display method and new positive pressure suction gun method, and the advantages and application effects of three improved and optimized leak detection methods in refuelling tank bottom plate leak detection are analyzed in detail; The types and causes of defects of the bottom plate are analyzed, and it is clear that the pasting method is an effective means of repair at the present stage. At the same time, it is pointed out that the problems need to be solved further.