Abstract: The GH4099 high-temperature alloy and T2 copper heterogeneous metal bonding was achieved by diffusion vacuum 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 joint formation quality, micromorphology, micro-area composition, hardness and tensile properties were investigated. The optimal process parameters window for diffusion vacuum welding under a smaller pressure （1.5−4.2 MPa） was determined. The results show that when the diffusion temperature was low, the weld was obvious and there were many continuous distributed hole defects, resulting in poor formation quality. When the diffusion temperature rose to 890 ℃ or above, there were no obvious hole defects. With the increase of diffusion temperature, diffusion pressure or holding time, the thickness of the diffusion layer at the connection interface increased. With the increase of diffusion temperature, the hardness of the high-temperature alloy base materia and the weld increased, the tensile strength of the joint first increased and then decreased. The diffusion pressure had a small effect on hardness and tensile strength. With the extension of holding time, the hardness of the high-temperature alloy base material increased, and the tensile strength of the joint increased. The optimal process parameters window for diffusion vacuum welding under small pressure （1.5−4.2 MPa） was diffusion temperature of 890 ℃ and holding time of 2 h, and the maximum hardness was 517 HV, the maximum tensile strength was 201 MPa.