In order to investigate the performance and modification mechanism of crumb rubber composite modified asphalt with chemical modifier，the conventional indexes such as softening point，5 ℃ ductility，elastic recovery rate，dynamic shear rheology test indexes are used to evaluated its performance. Compared with ordinary rubber-modified asphalt and SBS modified asphalt，the microscopic modification mechanism of crumb rubber composite modified asphalt was conducted by scanning electron microscope，Fourier infrared spectroscopy，and differential scanning calorimetry. The results show that crumb rubber composite modified asphalt has a higher failure temperature for performance grade（PG） of asphalt binder and shows better high-temperature performance. It can be known from the fluorescence microscope test，after 48 hours of storage，only some large rubber powder particles began to be adsorbed by the asphalt micelles and sank in the crumb rubber composite modified asphalt. After 72 hours of storage，the segregation has occurred obviously. Under the microscopic morphology, most of the rubber powders were evenly dispersed in the asphalt，arranged densely，and formed a sub-homogeneous structure in the crumb rubber composite modified asphalt. The infrared spectroscopy and the differential scanning calorimetry tests show that the physical blending modification and the chemical reaction existed simultaneously in the crumb rubber composite modified asphalt. Compared with a single physical modification, under the action of compound modification，the entire system appears a dense cross-linked network structure，which makes the intermolecular bonding firm，and performs better in terms of low-temperature properties.