The phenomenon of resonant tunneling through thin metal films with periodic narrow grooves is attributed to excitation of surface plasmon (SP) via the periodic structure coupler at the metal surface. In this paper, we will use the particle-in-cell (PIC) plasma simulation method to study the SP-mediated optical tunneling. The PIC method is a time-domain scheme to calculate self-consistently the interaction between the electromagnetic fields and the plasma particles. At the beginning of simulation, the mobile electrons and immobile positive ions are uniformly distributed in the thin Gaussian-shaped-grooved silver film with the plasma density calculated from silver's plasma frequency. The momentum collision-frequency method is employed to model the collision dissipation. For normally incident TM-polarized wave, the transmission coefficients peak at the SP resonant modes, similar to the results predicted by Drude model, except for with lower transmission coefficients. The variation of the averaged plasma energy with time exhibits some ripple-like patterns, which comes from the various competing processes of heating and cooling. But the temperature of the plasma has little effect on the transmission coefficient and the wave tunneling.