The effects of process parameters on vacuum diffusion bonding between tantalum (Ta) and copper (Cu) were studied. The interfacial structure of Ta/Cu joint was analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and microhardness test. The results indicate that under the condition of loading pressure of 10 MPa and holding time of 60 min, the number of interfacial voids decreases with increasing of bonding temperature. With the temperature up to 1000 °C, the voids at the interface disappear completely, the joint has the maximum shear strength, and its interfacial layer is about 3 to 5 μm. The microhardness test shows that the hardness in weld zone is relatively higher than that in non-weld zone due to the fact that work hardening takes place in the matrix and the joint interface