Singace fold model and Johnson Cook constitutive equation is used to study energy conversion process of interactions between impact objects and metal shell; material of strain strengthening effect, strain rate strengthening effect and temperature effect caused by impact load are considered. Angle increment fold method is put forward to calculate plastic deformation energy. According to system energy conservation composed of impact object and metal shell, analytical expressions of speed-displacement of impact object and instantaneous load-displacement between impact object and metal shell and temperature distribution function caused by metal shell plastic deformation are gained . Based on comparison between analysis of plastic deformation process under impact load with different material metal shell and finite element calculation result , validity of the calculation method is proved in this paper .