The invention discloses an asphalt viscosity reducer, as well as a preparation method and application thereof. The asphalt viscosity reducer comprises the following compounds in parts by weight: 10 to 19 parts of stearic acid, 2 to 5 parts of polyacrylic ester, 70 to 85 parts of fatty alcohol-polyoxyethylene ether and 4 to 16 parts of Carlo amine. The asphalt viscosity reducer obtained by mixing the above compounds uniformly at 90 to 100 DEG C and matrix asphalt are mixed to obtain an asphalt mixture; in the asphalt composition, the stearic acid has the effect of reducing surface tension so as to maintain the mixture to be uniform and stable, the polyacrylic ester has a good flocculation effect, the ether bond in the fatty alcohol-polyoxyethylene ether molecule is not liable to damage by acid and alkali, stable in performance, soluble in water and not liable to electrolysis, and the Carlo amine can effectively improve the adhesive force between the asphalt and aggregate, so as to improve the water stability of the mixed materials, prolong the service life of a road surface, and fulfill the aim of reducing the viscosity of the asphalt mixture.