The invention discloses a method for preparation of modified asphalt with SBS and waste rubber powder as the modifier. The method adopts a physics and chemistry combined technology, uses a coupling agent to conduct chemical treatment on the modifier surface, so that a coupling effect can be generated between SBS and waste rubber powder, under a synergistic effect of EVA, extrusion molding granulation is carried out to obtain waste rubber powder/SBS/EVA blend particles. The blend particles are added into asphalt, shearing dispersion is performed, under a synergistic effect of a cross-linking agent and an antiaging agent, the modified asphalt with excellent high-and-low temperature performance, aging resistance, high elastic recovery, high 60DEG C dynamic viscosity and high temperature storage performance can be obtained. The modified asphalt product is applicable to drainage road pavements, steel bridge deck paving and old pavement reconstruction stress absorbing layers. The raw materials used by the method have wide sources, can be produced on existing SBS modified asphalt devices, and new equipment investment is unnecessary. Therefore, the modified asphalt is suitable for industrialized production and long distance transport.