The invention relates to a preparation method of an expandable butadiene-styrene rubber powder microcapsule for asphalt. Firstly, an anionic styrene-butadiene latex is transformed into cationic styrene-butadiene latex through a transformation process, so that positive charges exist on the surface of the colloidal particles, large-particle-size butadiene-styrene colloidal particles of 100-200 Mum are formed by an attaching process, the butadiene-styrene colloidal particles are taken as microcapsule core materials, and monomers are added to be adsorbed on the surface of the colloidal particles,grafting reaction is carried out to form a microcapsule shell, and the microcapsule shell is subjected to condensation, granulation and drying to obtain the butadiene-styrene rubber powder microcapsule. The prepared butadiene-styrene rubber powder microcapsule can be used for isolating and preventing clustering, coagulation and the like, and can also be used in the modified asphalt process, the microcapsule is heated and then the shell comes off, the butadiene-styrene rubber is released and swelled in the asphalt, and the effect of modifying the asphalt is achieved.