Disclosed belongs to the technical field of heavy oil extraction, and specifically relates to a viscosity reduction system for microwave extraction of heavy oil and a preparation method thereof. The viscosity reduction system is a magnetic graphene oxide. The viscosity reduction system added to heavy oil has a significant viscosity reduction effect after microwave treatment. The viscosity reduction system exhibits lipophilicity and can be adsorbed on oil droplets, so that the thermal effect of microwaves assisted by the viscosity reduction system mainly acts on a reservoir, which reduces heat loss during heat transfer. At the same time, the viscosity reduction system is magnetic, which helps directional regulation and separation under the action of a magnetic field.