The dynamic responses of cerium under low pressure, including γ →α phase transition, are numerically studied in this paper. The velocity profiles of shock experiments show that the transition process between the two phases is smooth and there is no obvious disconnection between the two plastic waves of the particle velocity profiles. Three important problems in the dynamic response, including constitutive model, Hugoniot relation and phase transition/reversal, are discussed. A multi-phase equation of state and constitutive model of Ce are presented in this paper after analyzing the typical wave configuration of cerium under the shock loading and releasing. The dynamic phase transition model is built for the non-equilibrium course in the phase γ → α transition induced by shock wave. The numerical results accord with the experimental data of the plane impact tests, indicating that the dynamic phase transition model can describe the dynamic response under low pressure of cerium more reasonably.