The basic theories about structural sensitivity analysis are introduced

and the general method of structural optimization and sensitivity analysis based on the finite element method are presented.The finite element structural analysis model is established for a certain machine gun.The bending stiffness

torsion stiffness and the first inherent frequency are selected to form the performance restraints.According to the results of the sensitivity analysis and the demand of high stiffness and light mass

the effective design variables are chosen to optimize the mass and performance of structure

and these dynamical responses of weapon were simulated and contrasted between before and after the optimization by experimental testing results

which show that the matching between inherence vibration frequency and fire frequency becomes better

and the firing accuracy of a machine gun is improved.