Based on high pressure reactor as simulator of conditions in heavy oil recovery, use self-made Mo ultra-dispersed catalyst to carry out aquathermolysis of heavy oil with formamide as hydrogen donor. Investigated effects on heavy oil viscosity, group composition and elements content by adding hydrogen into these moments before and after the catalytic aquathermolysis reaction, and employ infrared spectrum and gas chromatography to analyse changes in the structures and composition of heavy oil at these moments before and after the catalytic aquathermolysis reaction with hydrogen donor. The results showed that, with the increase of mass fraction of hydrogen donor, heavy oil viscosity reduction rate increased, saturated hydrocarbon and aromatic hydrocarbon accrued, at the same time, contents of resin and asphaltene reduced. Under the synergy of catalyst and hydrogen donor, carbon content in the crude oil reduced, hydorgen content increased, and H/C atomic raiton increased, content of sulfur also decreased. The results of infrared spectrum and gas chromatography analysis showed that, after hydrothermal catalytic pyrolysis, the number of aromatic rings reduced, the content of ligh components increased, and the content of heavy compoents decreased, after oil upgraded, oil was further diluted by light hydrocarbon, which reduces the viscosity of crude oil system.