Abstract: Characteristic of the normal impact of cylindrical projectile onto LY12 aluminum Whipple shielding Concept within the first doorsill value are studied with an example of dual-sheet Whipple structure through experimental investigation.So,shielding Concept damage behaviors with projectile velocity are presented.Within the first doorsill value of normal impact,the change of velocity,thickness of shielding and target,prevention distance can deeply affect the results of shielding ang target.