Abstract: To analyze the nonlinear viscoelastic properties of modified asphalt, dynamic viscoelastic constitutive equations are studied, consisting of generalized Maxwell model and fractional calculus Maxwell model. The two kinds of constitutive equations are compared based on the fitting result. The result showing generalized Maxwell model can fit well the viscoelastic performance of modified asphalt except for both sides of the curve. Therefore, it is unsuitable to predict viscoelastic properties using generalized Maxwell model. It is concluded that the fractional calculus model can fit accurately the viscoelastic performance of modified asphalt and the fitting result can be used to evaluate the viscoelastic performance of modified asphalt.