By finite difference method, the evolvement of plasma generated by a pulsed laser is studied for pulsed laser deposition of KTa065Nb035O3(KTN) thin film. We have discussed the movement of particles in plasma in isothermal and adiabatic expansion stages in more detail. At the same time, we have simulated the change of figure of plasma at different time. Moreover, the physics mechanism in expansion of the plasma have been explained. The theoretical results are compared with our experiments and other author's conclusions.