Abstract: In view of difficult manufacture of the rotor component in the high-pressure plunger pump for aerospace, the connection between 25Cr3MoA steel and ZQSn10-2-3 copper was researched by vacuum diffusion bonding.The experiments based on different combinations of temperature-pressure-time were carried out to explore the effects of experiment parameters on the diffusion bonding effect. The tensile strength after diffusion was tested. Meanwhile, the morphology, microstructure and element distribution of the diffusion bonding joints were observed. The result shows that the quality of diffusion bonding joints under 830 ℃ -5.5 MPa is generally better, in which tensile strength under 830 ℃ -5.5 MPa -0.5 h is 295 MPa. With the extension of diffusion time, the thickness of the diffusion layer also increases. The second phase precipitates are dispersed in the diffusion layer, which hinders the movement of dislocations. However, with the increase of pressure, the steel/copper diffusion bonding effects become poor and even fail. When the temperature rises to 860 ℃, a phenomenon that material is crushing and melting during vacuum diffusion under 9.7 MPa high pressure occurs. At this time, the transient melting process between solid and liquid makes the second phase grow up, which occupies the whole diffusion layer.