In order to study the influence of the optimal butt structure on the firing accuracy of shoulder firing without support in standing position, a comparative analysis scheme of simulation and experiment on the firing accuracy was proposed. Based on the dynamic model of the man-gun system, the muzzle jump angle and the random dispersion curve of the interior ballistics were obtained by collaborative simulation with the tilt angle of the butt shoulder surface and the stiffness of the butt as the design optimization variables. The simulation results of vertical target dispersion R50 are compared with the experimental results, and the results are basically consistent, the error is less than 15%. The results show that when the 6° soft butt is adopted, the projectile dispersion is obviously optimized, and the scheme has a guiding role in optimizing the gun structure and ergonomic design in the man-gun system.