Belonging to the technical field of asphalt materials, the invention relates to a nano modified asphalt and a preparation method thereof, and solves the problems of poor durability and easy degradation of asphalt materials in the prior art. The nano modified asphalt comprises the following raw materials by mass: 100 parts of matrix asphalt; 1-5 parts of SBS; 0.5-6 parts of a nano-material; 0.5-4 parts of a surfactant; and 0-1 part of a cross-linking stabilizer. According to the nano modified asphalt and the preparation method thereof provided by the invention, the durability of pavement asphalt material is improved, the needle penetration, softening point, ductility and other indexes of the asphalt are improved, and the service life of the asphalt pavement is prolonged.