Abstract: 42CrMo steel and brass were joined by spark plasma sintering technique. The microstructure, composition and hardness distribution of the joint were studied, and the joint microstructure formation process was analyzed. The results show that a transition layer with width of 10-20 μm existed between the 42CrMo steel and the brass. The microstructure of the transition layer was uniform and fine. In the brass near the transition layer, the island-like structure zone with width of about 70 μm was observed. These island-like structures mainly consisted of solid solution of iron. Under a relatively high pressure, no cracks but a few voids were observed in the joint. The microhardness on cross-section of the joint showed a change of gradient. The diffusion depth of iron reached 90 μm, but the diffusion of copper was not obvious. The 42CrMo steel and brass had a diffusion bonding.