Abstract: The dissimilar maetal joining of GH4099 high-temperature alloy and T2 copper was carried out by vacuum diffusion welding. The effects of diffusion temperature （860, 890, 920 ℃）, diffusion pressure （1.5, 2.8, 4.2 MPa）, and holding time （0.5, 1.0, 2.0 h） on the formation quality, hardness, and tensile properties of the joint were studied. The optimal process parameters range for vacuum diffusion welding was determined. The results show that at the diffusion temperature of 860 ℃, the welding interface was obvious and there were many continuous distributed hole defects, resulting in poor formation quality. At the diffusion temperature of 890 ℃ or above, there were no obvious hole defects, and the welding quality was high. With the increase of diffusion temperature or diffusion pressure, the thickness of the diffusion layer at the connection interface increased. With the extension of holding time, the diffusion layer showed a staged evolution characteristic of rapid early thickening, then blocked, and then thickening again. With the increase of diffusion temperature, the hardness of the diffusion layer increased, and the tensile strength of the joint first increased and then decreased. The influence of diffusion pressure on hardness and tensile strength was small. With the extension of holding time, the tensile strength increased. The optimal process parameter range for vacuum diffusion welding was diffusion temperature of 890 ℃, holding time of 2 h, and diffusion pressure of 1.5−4.2 MPa. At this time, the joint interface at the connection showed a wavy shape, the center of the diffusion layer generated copper-rich solid solution, chromium-rich solid solution, and Ni-Si hard brittle phase, and the thickness of the diffusion layer was 13−20 μm, with the tensile strength higher than the copper base material.