The ballistic experiment of 30mm semi-AP obliquely penetrating ceramic/steel target is designed, and the image measurement method of impact angle, displacement and back plate deformation is proposed. The high-speed photography image sequences is measured based on digital image processing, and the effect of impact angle of oblique penetration is analyzed. The study shows that the impact angle will induce asymmetric effect in the projectile's penetration process, and the angle of yaw will gradually increase; under the same velocity condition, when the impact angle increases, the time of penetration will prolong, and the penetration performance will be reduced.