Polyphosphric acid (PPA) modified asphalt binders were produced in the laboratory using one base asphalt and four levels of PPA contents (0.6%, 1.0%, 1.5% and 2.0% by weight of base asphalt). Penetration test, softening point test, rotation viscosity test, creep test with bending beam rheometer (BBR) and four components test were carried out to study the performance of PPA modified asphalt binders and possible modification mechanism. The results indicate that the high-temperature performance of PPA modified asphalt binders are obviously improved and temperature susceptibility are decreased, but the low-temperature performance slightly decline compared with base asphalt. The PPA content has a very significant effect on softening point whereas it has no significant influence on low-temperature performance according to variance analysis (ANOVA). Finally, four components test reveals that the primary modification mechanism of PPA is the change of chemical composition of asphalt binder.