Abstract: Based on viscoelastic theory,the low temperature bending beam rheometer test (BBR) of asphalt with different mass fractions of poly phosphoric acid (PPA) modification (0.5wt%,1.0wt%,1.5wt%,1.0wt%) were carried out.The creep data from the low temperature BBR test was nonlinearyly fitted using the Burgers model,and low temperature performance index was determined using the four parameters of Burgers model (E₁,η₁ ,E₂ and η₂ Maxwell and Kelvin model of elastic modulus and viscosity coefficient),and so the low temperature performance of the PPA modified asphalt was analyzed.The results shows that the addition of PPA improves the viscosity and elasticity of asphalt,the relaxation time decreases in the asphalt,the stored energy reduces,the dissipation energy increases,and the stress relaxation ability is improved.At the same temperature,the PPA modified asphalt delays the time of asphalt into the creep stability period,but it was shortened with the temperature decreasing.The low temperature performance of asphalt improves with the addition of PPA,and the effect is better with more PPA contents.But the improvement degree reduces with the decrease of the temperature,and the differences between the effects of different mass fractions also become smaller.The PPA is suitable at the temperature above -24℃,while it is meaningless below -24℃.