The invention relates to a reaction type asphalt regenerating agent and a preparation method thereof. The preparation method comprises the following steps: adding petroleum asphalt, maleic anhydride and a Diels-Alder addition reaction catalyst into a reaction container, heating to 160-180 DEG C to carry out addition reaction for 8-12 hours, cooling a system to 70-80 DEG C, adding a polyurethane prepolymer and a chain extender, and continuing the thermal insulation reaction for 8-10 hours, then adding a fatty acid amide serving as a viscosity reducer, nonylphenol polyoxyethylene ether serving as a penetrating agent and an anti-aging agent, and mechanically stirring at 80-90 DEG C for 2-4 hours until the mixture is uniformly stirred, so as to obtain the reaction type asphalt regenerating agent. The reaction type asphalt regenerating agent provided by the invention is relatively low in viscosity, does not need to be heated in use, is convenient to construct, has a good restoration effect to the ductility of aged asphalt and can meet the performance requirement of unused asphalt; and furthermore, the use ratio of regenerated materials can be increased, and the water damage resistance of a prepared regenerated asphalt mixture is superior to that of a general regenerating agent.