Abstract: Aiming at the problem of valve stem fracture and failure in the industrial steam supply system of a power plant, the failure mechanism was studied by chemical composition analysis, tensile test at room temperature, impact test at room temperature, metallographic analysis, Vickers hardness test and fracture morphology observation. The results show that the main reasons for the fatigue fracture of the stem samples are the small radius of the thread bottom arc and the poor material status of the samples, which are easy to produce stress concentration and poor fatigue resistance. During the use of the valve, especially under the bad working conditions of small flow rate and large pressure difference, fatigue cracks are gradually initiated under the alternating stress caused by the impact of the working medium and extend to fracture.