Asphaltene aggregation is considered one of the key points to the viscosity rise of heavy oil, which will severely impact heavy oil recovery. In this study, Cu2+ grafted polymers with varying lengths of side alkyl chain were synthesized to participate in heavy oil upgrading, and the influence on viscosity reduction and asphaltene aggregation of heavy oil has been discussed. The polymer structures were characterized by H-1 nuclear magnetic resonance (H-1 NMR) and Fourier transform infrared (FT-IR) spectroscopy. Cu2+ content was measured by high-temperature ashing method. The upgrading experiments were carried out in autoclaves, and asphaltene aggregation behavior was determined by UV-vis spectroscopy, optical microscopy, and near-infrared (near-IR) oil analyzer. The results have shown that, besides the role of Cu2+ in upgrading the reaction, polymer chains showed a significant effect on viscosity reduction. In studies on asphaltene aggregation behavior, it was found that polymer can disperse asphaltene and inhibit its aggregation even after high-temperature treatment. Meanwhile, as a carrier, polymer's long carbon chains help Cu2+ to contact with or even insert into asphaltene and increase the chance for C-S bond and C-C bond cleavage. As a result, after upgrading with PC3, the viscosity reduction ratio of Lukeqin crude oil reaches 66.67%. The heavy components amount (the content of resin plus asphaltene) decreases by 9.95%.