Abstract: Modified asphalts by crumb rubber powder with different microwave treating time were prepared. The molecular weight distribution of toluene extract of the crumb rubber microwave treated was determined by gel permeation chromatography. The crumb rubber and asphalt in modified asphalt were separated by solvent extraction to further investigate the crosslinking degree of the crumb powder and rubber hydrocarbon content changes using TG-DTA. Results show that the property of the modified asphalt has significant relations with its solubility in toluene. The crumb powder treated with microwave 5min has the highest degree of degradation in asphalt, and forms banded structures. The crosslinking of part of the macromolecular are decomposed, producing medium-sized molecules. The modified asphalt by crumb powder treated 5 min has the highest ductility and penetration but slightly lower in softening point. However, if the microwave treatment time prolongs to 6 min, the crosslinking of the medium-sized molecules formed at 5 min treatment occurs again. It is discovered that the extent of crossliking of powder in modified asphalt first decreases and then increases as the microwave treating time prolongs, the lowest crosslinking appears at 4 min treatment. While the rubber hydrocarbon content presents a trend of first decrease and then increase, with 5 min treatment, the content is down to the lowest. Decreasing the crosslinking is advantageous for the light components in asphalt swelling into the powder inside, raising the heavier components content, and thus helpful to harden the modified asphalt. The small molecules produced by degradation can enter into and soften the asphalt and form an interface layer between powder and asphalt that enhances the interaction of them..