A two-degree-of-freedom (2-DOF) quarter vehicle fractional-order nonlinear model is presented to describe the suspension with viscoelastic material. A general calculation scheme for the 2-DOF incremental harmonic balance method (IHBM) for nonlinear systems with fractional order is derived. The nonlinear dynamic of the present model obtain is acquired by using this method. The accuracy of the proposed method is verified by comparing with the power series expansion method. Afterward, the effects of the various parameters on the dynamic performance are analyzed. Results show that the fractional-order parameters play very important roles in the amplitude-frequency response of the system.