Because of corrective mode, ballistic characteristics of trajectory correction projectile and that of common grenade are significantly different. Firing data error is not included in system error. Thus, the computational methods of common grenade demand are not suitable for trajectory correction projectile. In this paper, a mathematical model of shooting efficiency assessment and estimating method of trajectory correction projectile was introduced. Example analysis and simulation demonstrate that the method is practical. It can be used for ammunition demand calculation of trajectory correction projectiles.