To study the affection on the vibration of wheeled self-propelled gun chassis during running firing, a nonlinear shock absorber damper model was built in this paper based on the basic theory of fluid and hydraulic mechanics. And the damping coefficient and stiffness coefficient expressions of the shock absorber were deduced, with its nonlinear damping characteristics included. In addition, according to the specific structural characteristics of wheeled self-propelled gun, expressions to calculate equivalent damp coefficient and equivalent stiffness coefficient were developed. And tests on wheeled self-propelled gun during running firing were done. Based on the tests data and the theory developed, numerical simulations in two conditions, the damping and stiffness coefficient calculated by linear expressions and by nonlinear expressions, were done respectively. The result shows that, simulations in the nonlinear condition match well with the experiments data, but simulations in the linear condition have a deviation to the experiments data. As a conclusion, the damping coefficient and stiffness coefficient has a considerable affection on the vibration of wheeled self-propelled gun chassis. This method can be popularized to studies on the simulation of vibration of other gun chassis.