In order to reduce the force transmitted from the upper carriage of a Truck-mounted howitzer to the lower carriage, the upper carriage is optimized for structural parameters under the premise that the position of the trunnion chamber is allowed to change. Based on the secondary development function of ABAQUS, established the parametric modeling script of the upper carriage structural, and built the ABAQUS computing environment through the integration of Simcode components of the ISIGHT platform. The position parameters of the trunnion chamber on the upper carriage were selected as the design variables, and the maximum support reaction force was minimized as the optimization objective. The multi-island genetic algorithm was used to optimize the structure parameters of the upper carriage under multiple working conditions, and the global optimal solution was obtained. The optimization results meet the rigidity and strength requirements, and the optimization effect is obvious. This optimization method can be used in the design of the upper carriage structure, reducing the force transmitted from the upper carriage of the artillery to the lower carriage, and can provide a certain optimization space for the weight reduction of the lower carriage, and has engineering application value.