In order to obtain the influence of structural parameters on the firing stability of the lightweight towed howitzer, the corresponding nonlinear finite element models were established. Nonlinear factors, such as contact/collision between the spade and soil, plastic deformation of soil, were considered in the finite element models. By solving the finite element models with different structural parameters, the structural parameters which have great influence on firing stability can be identified. Based on this, the optimization of firing stability was performed. The calculated results show that the optimized firing stability of the lightweight towed howitzer is improved.