The reasons leading to interior leakage of the manual globe valve used in a nuclear power plant during operation was analyzed by means of morphology analysis,hardness test,metallographic test,SEM and other detection means. The results showed that the metal loss of valve base and valve seal surfacing occured under the action of high temperature and high pressure gas-liquid flow,and the poor quality of surfacing on the sealing surface accelerates the internal leakage of the valve. It is recommended to strictly control the quality of the valve,especially the quality of sealing surface,to ensure that the size of the surfacing layer can meet the product design requirements.