Abstract: To study the constitutive property, fiber reinforced asphalt concrete is considered as a two-phase composite material. It contains asphalt concrete as the viscoelastic matrix, and fibers as the elastic inclusions. Based on the micromechanical model of effective moduli for composite materials, the secant effective relaxation moduli of fiber reinforced asphalt concrete are established. Using the new model, this paper analyzes the effective moduli of polymer fiber reinforced asphalt concrete theoretically. To make a comparison, the FE simulation of the concrete behavior considering creep effect is also performed. It is demonstrated that the present model can satisfactorily describe the viscoelastic behavior of fiber reinforced asphalt concrete. Finally, a FE analysis of pavement deflection is conducted by using the present constitutive model, showing that the intermingle of polymer fibers in asphalt concrete improves efficiently viscelastic property of pavements.