By way of Coupling the effects among the electric field, magnetic field and flow field in the pulsed plasma thruster, the process of the capacitor discharge, propellant ablation and plasma acceleration are characterized, and a one-dimensional time-dependent model based magnetohydrodynamic（MHD）for PPT is presented in this paper. The simulation results are analyzed and compared with the experiment. The result exhibits that the model perfectly reveals the thruster discharge process, variation of ablated mass and surface temperature of propellant.