Abstract: The vacuum brazing of YG8/42CrMo steel was studied with different process parameters such as brazing temperature and joint gap.A self-developed CuMnNi alloy was used as filler metal.Microstructure,wetting angle and 3 points bending strength of the brazed joints were analyzed by SEM,EPMA,EDS,contact angle meter and electronic universal testing machine.The results showed that this brazing filler metal had a good wettability to the two baseplates,and the optimum brazing temperature was 1 030 ℃.When the joint was brazed at 1 030 ℃ and the joint gap was 0.3 mm the bending strength of joints reached a maximum value of 510 MPa.FeCoNi single-phase solid solution could be achieved by long range diffusion of Co,Fe and Ni in the interface,which could benefit the metallurgical combination joint and improve the mechanical properties.