The vaporization effect and the following plasma shielding generated by high-power nanosecond pulsed laser ablation are studied in detail based on the heat flux equation. As an example of Si target, we obtain the time evolution of the calculated surface temperature, ablation rate and ablation depth by solving the heat flow equations using a finite difference method. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the variation of ablation depth per pulse with laser fluence is performed. Our numerical results are more agreed with the experiment datum than other simulated results. The result shows that the plasma shielding is very important. (C) 2007 Elsevier B.V. All rights reserved.