Abstract: Based on Alekseevski-Tate model, the present paper theoretically analyses the interface defeat of a conical-nosed projectile in its penetration process and the corresponding formulae of velocity decay and mass erosion of projectile are conducted out. The effects of half apex angle on the kinetic energy loss of conical-nosed projectile are discussed, and comparison between the kinetic energy loss of conical-nosed projectile and that of flat-nosed long rod is declared.