The internal ballistics process of electromagnetic railgun launch is an extreme multi-physics field strong coupling process. The projectile guidance section is a key component affecting the maintenance of the projectile’s internal ballistics attitude. However, there is little research on the internal ballistics-related design and optimization of the guidance. This paper establishes a multi-physics field coupling simulation model for the internal ballistics of electromagnetic railgun launch, analyzing the electrical, magnetic, thermal, and mechanical system responses of the armature-projectile. The response characteristics of the projectile armature’s acceleration during the internal ballistics stage in the time and frequency domains are analyzed, and a standard for evaluating internal ballistics attitude stability using the peak-to-peak value of lateral acceleration is proposed. Based on this objective and combined with the weight requirements of the guidance section, multi-objective optimization of the structural parameters of the guidance section is conducted. The Pareto solutions of the parameters are obtained using the ANN-RSM method, and qualitative verification is performed through experiments. The results show that the optimization effect is good and effective.