Abstract: A new debris cloud model based on the largest fragment theory is put forward. It is assumed that the debris cloud is split into the debris cloud of bumper, the debris cloud of projectile and the largest fragment of projectile. All debris clouds originating from the projectile and the fragments originating from the bumper plate are evenly distributed on the surface of a big and a small expanding spherical shells, respectively. The largest fragment is located on the shot axis of the leading edge of the two spherical shells. The comparison of this new model with the Schonberg model and the Swift model shows that the new model is simple, accurate and applicable in a wide range. This model can provide an effective guidance for design and performance analysis of the spacecraft shielding structure.