Composite structures of copper and stainless steel are often used in nuclear island cooling system. Copper conducts heat quickly,the heat generated by the nuclear reaction can be rapidly transferred to the stainless steel tube through copper. The cooling medium introduced into the stainless steel tube takes away the heat immediately to ensure the safety of the nuclear power system.Therefore,the welding quality of copper and stainless steel pipes plays an important role in the nuclear island cooling system. The welding procedure design of vacuum brazing of T2 pure copper and 316L austenitic stainless steel tube is conducted. For the joints with high precision gap,silver-copper eutectic solder is used,and brazing is carried out under vacuum of 8×10,-3, Pa with heat preservation of 830 ℃ for 30 min. Microstructure observation and performance analysis of brazed joints are studied by shear test,metallographic microscope,micro-hardness test,thermal shock test,scanning electron microscope（SEM） and energy dispersive spectrometer（EDS）. The result shows that stainless steel and copper are successfully joined together and the brazing seam is dense. The microstructures in the middle area of the brazing seam are copper-based solid solutions and silver-copper eutectic. The shear strength of brazed joints can reach 176 MPa. The shear fracture location is in the brazing seam,and the fracture type is ductile fracture.