Abstract: Cu-Si alloy powder was prepared by induction furnace melting and water atomization process, and the Si₃N₄ in-situ reinforced Cu matrix composites (Si₃N₄/Cu) were prepared after gas mixture of N₂ and H₂ selective nitriding and vacuum spark plasma sintering (SPS) forming. The selective nitriding product and its crystalline structure were investigated by extraction method. Results show that nitrogen content of composite powder rises with the increase of nitriding temperature and extension of nitriding time. The nitrogen content significantly increases after nitriding for more than 60 h under 1 000 ℃. Overall diffraction peaks of Cu apparently move to the big angle, and the lattice constant decreases at the same time, which suggest that Si exsolves from Cu matrix to form Si₃N₄ while reacts with N. The reinforcement in Si₃N₄/Cu composites is mainly β-Si₃N₄. With nitriding temperature and time increasing, the electrical conductivity and hardness of Si₃N₄/Cu composites gradually increase.