Abstract: Based on the bending bean rheometer test (BBR) and DSC measurement of the glass transition temperature,the low temperature properties of asphalt with different dosage of poly phosphoric acid (PPA) and SBS-PPA were studied.The effect of PPA content on the performance of asphalt at low temperature was analyzed using the method of single factor variance.The phase structure characteristics of SBS-PPA composite modified asphalt were observed and analyzed by fluorescence microscope.The results shows that PPA addition can improve the low temperature performance of matrix asphalt and SBS modified asphalt,and with the increase of PPA content,low temperature anti-crack performance of bitumen is better.But with the decrease of temperature,the effect of low temperature improvement is gradually reduced.Effect degree of PPA on the properties of base asphalt at low temperature is different at different temperature.At the temperature of -18--12℃,PPA has significant effects on the low temperature performance of base asphalt.At the temperature of -30--24℃,PPA has no significant impact on the low temperature performance of base asphalt.While the effect of PPA on the low temperature performance of SBS-PPA modified asphalt at different temperatures is not significant.The low temperature anti-crack performance of SBS-PPA modified bitumen is better than that of PPA modified asphalt,and the addition of PPA can effectively promote the SBS to disperse into small particles and become more uniform distribution in the asphalt,so the storage stability and the space mesh structure of SBS modified asphalt can be improved effectively.