In this study, an elasto-plastic constitutive model is presented to study the behavior of partially saturated clay under impact loading. In plasticity, a modified Mohr-Coulomb yield function is adopted. The cohesion and internal frictional angle of clay are calculated through static experiment. Based on the experimental investigations at different strain rates by means of split Hopkinson pressure bar (SHPB), the Mohr Coulomb criterion is modified by taking into account the effect of strain rate, and the parameters are determined.