Under the condition of high pressure reactor simulating oil reservoirs thermal recovery, with the catalyst of selfmade organic oil-soluble salt, with the hydrogen donor of formic acid, the study of catalytic aquathermolysis of heavy oil has been carried out. The effects of adding hydrogen donor on the viscosity, group composition and sulfur content of heavy oil have been investigated and the thermal conversion behavior of the asphaltene of heavy oil have been analyzed by the method of TG-DTA analysis before and after the catalytic aquathermolysis reaction. It turns out that, with the increase of the mass fraction of hydrogen donor, the viscosity reduction ratio, the contents of saturated hydrocarbons and aromatic hydrocarbons are going up while the contents of resin and asphaltenes are reducing after the hydrogen donor catalytic aquathermolysis reaction. Then under the combined effect of catalysts and hydrogen donor, the amount of carbon and sulfur dropped, the amount of hydrogen increased, so the proportion of H/C atomic number becomes higher. According to the TG-DTA curve of asphaltenes in the heavy oil, the weight loss of asphaltenes in the heavy oil after the hydrogen donor catalytic aquathermolysis reaction is higher than that of before the reaction, which means the stability of the asphaltene in heavy oil has been weakened after the hydrogen donor catalytic aquathermolysis reaction.