A preparation method of a waterproof agent for water-borne light oil comprises the following steps: S1, weighing paraffin wax, white oil, cera alba, carbo wax, stearic acid, water and morpholine, heating to boil in a reaction container, stirring until each component melts uniformly to form a mixture, and insulating at 100 DEG C for 30min; and S2, cooling the mixture to 80-95 DEG C, homogenizing the mixture under the pressure of 20-35MPa by using a homogenizer to blast the large particles into small particles, and finally rapidly cooling water to obtain the proofing agent. The invention also provides the waterproof agent for the water-borne light oil obtained by the method.