Abstract: The steam control valve stem in a turbine was broken during disassembling and inspection. The reason for the break of valve stem was analyzed by macroscopic observation, chemical composition analysis, mechanical performance test, fracture analysis, energy spectrum analysis, microstructure observation and hardness test. The results showed that valve stem had corrosion pits and stress corrosion cracks at steam inlet. According to the use environment and actual use of valve stem, it was considered that valve stem was a one-time fracture during stoppage test.