Abstract: This paper illustrates the reaction pattern of catalytic oxidative degradation of macromolecule constituents in heavy viscose oil.Parameters, include reaction time, catalyst system and the catalytic function of the oil-bearing layer minerals at various conditions that affect the change in viscosity and average molecular mass of the heavy oil, were investigated in detail. It was found that in the ［(MoO₂)(acac)₂］/t-BuOOH/H₃PO₄/oil-bearing layer minerals system, the degradation of asphaltenes reached 81%, the viscosity of heavy oil fell from 117.2 Pa·s to 55.8 Pa·s, reduced by 52.4% and the average molecular mass fell by 100.The TLC-FID analysis indicated that the asphaltenes in heavy oil were transformed into resin, aromatics and saturates.The resulting physico-chemical changes enhanced the stability of the oil system.It could be beneficial in the exploitation, transportation and processing of heavy oil.