Composite flame retardant and smoke suppressant was prepared by using aluminum hydroxide， organic montmorillonite and expandable graphite. By the limiting oxygen index（LOI） method， oven constant temperature heating， thermogravimetric analysis， Fourier infrared spectroscopy， scanning electron microscopy and X-ray energy spectrum were used to analyze the effect and synergistic mechanism of composite flame retardant and smoke suppressant for asphalt. The results show that the addition of the compound agent has obvious flame retardant and smoke suppression effect， 6% of the compound agent can increase the LOI value of asphalt to 25.19%， and the unit asphalt smoke release amount is reduced by 70% . The compound agent broadens the temperature range of the single combustion promoter. It absorbs heat and dilutes the concentration of combustible gas during the combustion of asphalt. It not only improves the thermal stability of asphalt， but also forms a composite barrier layer， which plays a synergistic flame retardant and smoke suppression role.