Abstract: Leakage reason of copper valves during hydraulic pressure test process was analyzed by using scanning electron microscope and its accompanying X-ray energy spectrometer. The results show that there were defects in the raw materials of the valves. There was a large number of Pb element segregation in the material, which resulted in the formation of defects such as porosities and holes around the Pb element segregation zone. These kinds of defects decreased the strength of the copper valves, so water leaked easily at the defect zone when the pressure increased to a certain degree.