Abstract: The field test for viscosity reduction of Tahe TH12196 heavy oil by hydrothermal catalytic process was conducted in the pilot plant of Northwest Oilfield Company, Sinopec using a catalytic viscosity reducer developed by Research Institute of Petroleum Processing. The results show that the viscosity of Tahe oil is reduced by 54.5% after catalytic modification at the conditions of reaction time of 6h, 160℃ and the viscosity reducer dosage of 1.5%, 51.4% more than that of hydrothermal method, while similar to the results of laboratory. After the modification, the heavy components are decreased and the light ones are increased. The breakage of weaker chemical bond between molecules leads the composition changes of heavy oil, resulting in smaller aggregations and irreversible viscosity reduction.