Abstract: Due to the valve stem material, improper heat treatment, stress concentration, pitting, intergranular corrosion and other factors in the valve opening and closing process, the fracture event often occurs, which affects the safe operation of nuclear power units. In order to solve the problem that the maintenance workload of the stop valve in nuclear power plant is large and it can’t be reused after disassembly and inspection, this paper develops a special aging detection technology for micro-cracks in the stop valve stem, realizes the effective detection of microcracks in the sensitive parts of the valve stem fracture, and reduces the workload in the valve maintenance process.