The invention discloses warm mix asphalt and a preparation method thereof. A formula of the warm mix asphalt comprises a powdered solid material, a branched high-molecular polymer, an oleophylic surfactant, stearic acid and matrix asphalt, wherein the powdered solid material is a separated solid product obtained by conducting oily sludge hot extraction and dewatering technology treatment on oily sludge. According to the warm mix asphalt, all components act synergistically, the effect of additive synergism can be achieved, mixing temperature and forming temperature of a warm mix asphalt mixture prepared form the warm mix asphalt are both lower than 135 DEG C, the warm mix asphalt mixture has the advantages of obviously decreasing the mixing temperature and forming temperature, and various properties of the warm mix asphalt mixture are equivalent to those of hot mix asphalt.