From the relation between damage probability and density of surface inclusion, combining with the test results of XRD and laser induced damage, we have drawn a conclusion that bulk inclusions dominate the damage in these experiments. Combining thermal and mechanical processes of inclusion absorption and the statistical rule of inclusion density, we have deduced an equation describing the relation between damage probability and density of inclusions, power density of laser pulse, as well as thickness of films. From the model in this paper, we can see that the range of siges in which the inclusions can initialize damage alter with the depth of inclusions. So density of the dangerous inclusions in different depth is different. The results from theory and from experiments are identical. This model can also interpret damage morphology.