In order to clarify the effect of heavy oil hydrothermal cracking temperature at 250 ℃ and 280 ℃ on the molecular structure of asphaltene and the viscosity of heavy oil under the catalysis of amphiphilic catalyst，taking Shengli heavy oil as the research object and C₁₂BSNi as the catalyst，the changes of asphaltene molecular structure before and after the reaction were analyzed by FTIR and 1H-NMR. The results showed that when the hydrocracking reaction of heavy oil occurred at the temperature of 250 ℃，the viscosity of heavy oil was greatly reduced，the viscosity reduction rate being of 60.4%，while the viscosity reduction rate decreased with the increase of reaction temperature to 280 ℃，viscosity reduction rate only being of 53.8%. As the reaction temperature increased from 250 ℃ to 280 ℃，the average side chain length of asphaltene molecules gradually decreased，but the aromaticity increased and the number of aromatic rings increased，which indicated that asphaltene molecules had undergone radical condensation reactions，and the average molecular structure of asphaltene became larger，resulting in a relatively small viscosity reduction rate. In addition，a series of bond breaking reactions occurred during the reaction of asphaltene molecules，resulting in the reduction of their steric hindrance. The smaller the asphaltene molecular unit lamella，the easier it was to accumulate. It was observed by SEM that the pore channel of asphaltene structure gradually became larger and denser with the increase of temperature， but the surface aggregated particles became larger. It provided important guiding significance for the optimization of operating conditions of heavy oil hydrothermal cracking reaction.