<p>To explore influences from drive current on the projectile launched speed, and the spacing and width of rails on the maximum value of current in the electromagnetic gun. The motion equation of plasma armature is analyzed by the Newton method. In this paper, considering armature motion subjected to plasma viscous drag and inertial drag, the optimization model between armature speed and drive current was built. The results showed that the projectile launched speed would get the maximum value when the drive current was the specific value. Moreover, the influences from spacing and width of rails on the maximum value of current and the projectile launched speed were proved. Therefore, the optimization model that was built by the Newton method research the electromagnetic railgun is of great significance.</p>