This paper presents an improved model for the critical impact yaw (or simply the critical yaw) in long-rod penetration with considering the deceleration and rotation of the rod and the crater shape of the target. Two critical yaws, and , under normal impact were identified, below which there is no contact between the rod and crater sidewall (for ) and between the rod and the crater entrance (for ) during the entire penetration process. Contact functions and iterative algorithms were proposed in order to obtain these two critical yaws numerically. The influences of four dominant nondimensional numbers (i.e., the ratio of the target resistance to the rod strength , Johnson's damage number of the rod , square root of the target–projectile density ratio , and the diameter–length ratio of the rod ) on two critical yaws were studied for three typical rod–target systems (tungsten alloy rods penetrating steel targets, steel rods penetrating aluminum alloy targets, and steel rods penetrating steel targets). The relationship between two critical yaw angles was also discussed. A new empirical formula for the critical yaw was proposed based on the parametric study results and dominant nondimensional numbers, which extends the valid application range of the existing empirical formula.