Electromagnetic projectile launch uses electromagnetic force. After the armature exits the barrel, the leftover energy in the launch system is released via the muzzle plasma arc. This high-energy arcing can harm the launch system. To grasp the muzzle plasma arc’s development and its impact on the muzzle environment, this paper employs fluid simulation software. For a 16 mm-caliber launch system, combining magnetohydrodynamics with user - defined functions (UDF), a 2D fluid - structure interaction model is built, achieving multiphysics coupling of electromagnetic, flow, and thermal fields. The simulated potential difference between the guide rails matches experimental data, showing the simulation’s reliability. Results indicate that the muzzle plasma arc gradually transfers from the plasma arc circuit to the guide rail circuit, and it has a relatively stable phase. Its high temperature and shock waves expand inward and outward. The outward shock wave alters the initial muzzle flow field, while the inward expansion causes reverse airflow and blowback. After briefly reversing, the internal airflow moves outward again. This aligns with experiments where molten metal is ejected as the plasma arc fades. These findings offer theoretical support for muzzle material/structure selection, dynamic launch experiments, protection design, and electromagnetic launch interior ballistics research.