Abstract: Through laboratory experiments with samples from Daqing and Liaohe oilfields, the effects of reservoir mineral, NiSO4 and tetrahydronaphthalene (THN) on the aquathermolysis (AT) of heavy oil were investigated. The results indicate that, in contrast with simple AT, the addition of reservoir minerals leads to lower average molecular weight, higher contents of saturated and aromatic hydrocarbon fractions and lower contents of resin and asphaltene fractions, and the viscosity reduction ratio of the two oil samples increases from 7.41% and 12.95% to 16.05% and 25.29% respectively, which means that reservoir minerals can catalyze the AT of heavy oil. With the addition of NiSO4 and THN into the reaction system, the average molecular weight of the reaction products decreases further, the contents of saturated and aromatic hydrocarbon fractions increase and the contents of resin and asphaltene fractions decrease further, the viscosity decreases greatly with a reduction ratio as high as 84.39%.