The theory and method of asphalt fireretardant surface modified with silane coupling agent is introduced and the optimum silane dosage is determined. The structure and performance of asphalt fireretardant before and after the surface modification is characterized through infrared spectrum and thermo gravimetric analysis. Dispersion effect of asphalt fireretardant before and after the surface modification is studied and the influence of surface modification on the hydrophilicity and lipophilicity of asphalt fireretardant is analysed contrastively. It is shown that obvious physical and chemical action occur between silane coupling agent and asphalt fireretardant, which reduce the surface polarity of asphalt fire retardant with the optimum dosage of 0.95% for the asphalt fire retardant. And Surface modification strengthens the thermal stability, dispersibility and lipophilicity of asphalt fireretardant so as to improve compatibility of asphalt and asphalt fireretardant.