In order to investigate the feasibility of viscosity reduction of offshore heavy oil by catalytic upgrading，and to resolve the problems in the process of artificial lift and gathering and transportation，targeting a heavy oil in the western Bohai Bay，the relationship between viscosity and SARA of heavy oil was analyzed. Ten catalysts，composed of two anion，PAS and FAS，and five cation，Zn²⁺，Cu²⁺，Mn²⁺、Fe³⁺ and Ni²⁺，were used to carry out catalytic upgrading test，and the catalytic upgrading effect was evaluated by comparing SARA of heavy oil before and after upgrading. The result of experiments indicated that the viscosity of the Bohai heavy oil declined with the increase of saturates content and aromatics content and grew with the increase of resin content and asphaltene content. Saturates content had more influence on viscosity compared to aromatics content，and asphaltene content had a little bit more influence on viscosity than aromatics content. Considering resin took a big proportion，decreasing resin content was the primary target of reducing viscosity of the heavy oil. The catalytic upgrading effect of PAS-Ni was the best，as viscosity was reduced from 2167 mPa·s to 566 mPa·s with reduction rate of 73.88%. Followed by PAS-Fe，as viscosity was reduced to 716 mPa·s with reduction rate of 66.96%. SARA analysis of the upgraded heavy oil showed that the resin content dramatically dropped，and saturates content and aromatics content rose，while asphaltene content slightly increased.