This paper is focused on controller parameterization method of H_infinity control for a vehicle model with active suspension system, which involves internal stability and external disturbance attenuation. One of aims of this paper is to design a controller with parameters by Hamiltonian function method to insure that the vehicle dynamic system is established with a focus on handing the trade-off of constraints on the heave and pitch acceleration, suspension deflections, the other one propose an algorithm for solving parameters of the controller with symbolic computation. The proposed parameterization method avoids solving Hamilton-Jacobi-Issacs equations, and thus the obtained controllers with parameters are relatively simple in form and easy in operation. Simulation with a quarter-vehicle model shows that the controller is effective as it can optimize control by adjusting the parameters.