Styrene-butadiene latex with high rubber content was prepared by high-low temperature composite process using butadiene and styrene. Then powdered styrene-butadiene rubber (PSBR) with uniform particle size distribution (<1 mm) was prepared by coagulation method. The coagulation mechanism and preparation technology of powdered styrene-butadiene rubber were investigated. Furthermore, the morphology of the rubber powder was observed by polarized light microscopy. The results showed that the flocculation agent, coagulant and isolating agent in the coagulation stage have the greatest influence on the morphology of PSBR. A mixture of sodium stearate, sodium oleate and simethicone was the best isolating agent. When the addition amount of sodium chloride as flocculant was 1.3% (based on the mass of latex, the same below) and that of magnesium sulfate as coagulant was 2.5%, the PSBR had uniform particle size. The prepared PSBR was used to modify 70# matrix asphalt. When the additive content of PSBR was 1% of the mass of asphalt, the softening point of the modified asphalt was 51.8℃, higher than that of 70# matrix asphalt (47.6℃). The modified asphalt prepared in this paper showed a 5℃elongation of over 100 cm, better than any market samples of powdered styrene-butadiene rubber in modifying asphalt process.