This paper applies high-pressure reactor to simulate conditions of thermal recovery and uses formic acid as hydrogen donor body, self-made oil-soluble organic nickel salt as catalyst and urea as auxiliary agents to conduct the study on of heavy oil. By TG-DTA, IR and NMR spectra, it makes an analysis on thermal transformation behavior and structural changes of asphaltine in heavy oil before and after the reaction of upgrading and viscosity reduction under the effect of auxiliary agents. The results show that the stability of the asphaltine in heavy oil after aquathermolysis reaction of hydrogen donor catalyzing is decreased. Infrared spectroscopy analysis reveals that the absorption peaks of IR functional groups of asphaltine in heavy oil is unchanged and the addition of auxiliary agents basically does not change the structure of asphaltine. NMR structural analysis shows that.