The invention provides SBS (stimulated brillouin scattering) modified asphalt and preparation method thereof, belonging to the technical field of road materials. The method comprises the following steps of: by utilizing heavy traffic paving asphalt as a raw material, melting and heating the heavy traffic paving asphalt to 180-200 DEG C, and then, adding an SBS modifier, three line cutting furfural extract oil and polyphosphoric acid into the smelted heavy traffic paving asphalt, shearing, adding a stabilizer, developing and stirring to prepare the SBS modified asphalt. According to the preparation method, the SBS modifier and the polyphosphoric acid are added to modify the heavy traffic paving asphalt, namely, the polyphosphoric acid substitutes a part of SBS modifier, so that the addition dosage of the SBS modifier can be reduced under a consistent part by weight of the heavy traffic paving asphalt, the addition dosage of the SBS modifier can be reduced for about 1-2%, the polyphosphoric acid is added to change the structure of the modified asphalt, the softening point of the prepared modified asphalt is higher than 80 DEG C, and other performance indexes meet related standards for different grades of SBS modified asphalt by the Ministry of transportation. The technique is simple, convenient to operate and suitable for industrial production.