The Earth penetration weapon (EPW) is usually designed with a large length-diameter ratio to achieve high penetration ability, while structural stability decreases accordingly. However, existing penetration theories inaccurately describe the critical section position of the projectile where fracture occurs during oblique penetration. In this study, a free-free beam model is adopted to analyze the mechanical behavior of EPW under transverse loads induced by oblique penetration, focusing on the effects of mass distribution and two typical load modes (point load and distributed load). The results demonstrated that the critical section position was affected by both mass distribution and the load mode. Under equal mass conditions, the movement direction of the critical section was consistent with the center of mass, and shifting the mass center towards the head enhanced structural bending resistance. The bending moment state of the projectile under the distributed load shows better agreement with experimental results than that under the point load. The critical section forms at the front third of the projectile and shifts rearward as the distributed load length increases. A theoretical formula was proposed for bending moment calculation that can be used for projectiles with known shapes. The research content and results provide the theoretical basis for structural design and the bending failure of the projectile.