Abstract: This paper analyzes the radial response of a target due to the penetration of the shaped charge jets. The radius variation of the jet in the motion process is deduced based on the virtual origin concept. The variation of the cavity radius in the penetrating process is analyzed, and a theoretical model to describe the relation between the cavity radius and penetration, and the relation between the cavity radius and time, is developed based on the quasi-steady hydrodynamic penetration theory. A comparison between predicted results and experimental results demonstrates better agreement. This study may provide valuable references to engineering practice.