Abstract: This paper first introduces the aquathermolysis of heavy oil and its reaction mechanism, and based upon which discusses the enhanced effect of chemical agents on the aquathermolysis. It continues to review the research progress at home and abroad using catalyst, hydrogen donor and additives to enhance viscosity reduction of heavy oil by aquathermolysis. Finally the paper points out that the research trends are; developing cheap catalyst with high activity, selectivity and broad reaction condition on the basis of specific reservoir mineral and heavy oil, seeking for high efficient hydrogen donor with rich sources and industrialization prospect, selection of optimum additives like surfactant to make full use of the synergetic effect such as emulsification-viscosity-reduction, combination with the technologies of water shut-off and profile control to give full play to the function of chemical agents.