Abstract: The effect of microwave radiation parameters（temperature，power and time） on viscosity reduction，desulfurization, group composition, removal of metal impurities was studied using Saudi Arabian medium crude residue（SZ）as a raw material. The results show that in the experimental condition range，viscosity of radiated product first decreases and then increases with increasing of temperature and radiation time; While it decreases with increase of the power. Sulfur content goes down gradually with the increase of the power. Saturated hydrocarbon and metal (Ni，V) contents basically remain unchanged; The content of aromatic hydrocarbon increases slightly; Resin and asphaltene decrease. Finally, the influence rule of the nature of three kinds of residues: SZ, Saudi Arabian light crude residue (SQ) and Jinling residue (JL) on the viscosity reduction treated by microwave was investigated. The results show that the more the asphaltene in feeds，the better the effect of viscosity reduction.