Long term exposure to whole-body vibration results in driver’s fatigue and low-back-pain, especially for those people who are driving commercial vehicles like trucks and tractors. Seat suspension system becomes an effective and available option to improve the ride comfort of drivers. In this paper, a method of obtaining excitation spectrum based on virtual iteration technique is proposed to optimize the vibration transfer functions of commercial vehicle seat suspension system. Acceleration transducer are used to measure the acceleration signal of driver’s seat base and frame under different speed and road conditions such as national highway and expressway. A multi-body dynamic model of commercial vehicle seat suspension system is established according to the parameters of the seat suspension system in which the air spring and the oil damper are used to reduce vibration transfer. A virtual iteration program is developed to obtain a real displacement excitation on seat base. In this program, the nonlinear transfer function of the seat suspension system is solved by means of white noise as the initial input, and the real road acceleration spectrum signal under different speed and road conditions is used as the target of virtual iteration respectively. Once the real road spectrum signal is achieved, virtual iteration is completed, then a displacement excitation satisfying the accuracy requirement under commercial vehicle driver’s seat base is derived. Time domain characteristics, frequency domain characteristics and the value of relative damage are used to judge the convergence of the virtual iteration. The results show that accurate seat displacement drive can be obtained using the virtual iteration method proposed and the optimization of seat suspension system can be further completed to improve the ride comfort of drivers in commercial vehicle.