Using a two_fluid two_temperature hydrodynamic code, we studied the hydrodynamic s in the interaction of intense (1015W/cm2) ultrashort (150fs) laser pulses and linear density plasmas. The simulation results show the ponderomotiv e force effect on the formation of the electron density ripples in underdense re gion, such ripples increase the reflection of the laser pulse, and on the separa tion of the plasma in critical surface. Quasi_electroneutrality is not suitable in this case because of the different ponderomotive force and the gradient of th ermal_pressure for ions and electrons. Ions are moved by the electrostatic force . Comparing with the simulation results from one_fluid two_temperature code, we find that under strong ponderomotive force and gradient of thermo_pressure, two_ fluid code is more suitable to simulate the hydrodynamics of plasmas.