Basing the experiment phenomenon, a model and criterion for simulating mechanics erosion process have been developed for laser irradiating glass/epoxy composite. The mechanics erosion process has been divided into two processes of delamination and layer fracture. A thermo mechanical model can be used until composite delamination appears. Then plates and shell theory can be used for simulating layer fracture. The experiment results agree well with the simulation value , and that shows the model is reasonable. The simulation results indicate that the mechanics erosion process is very important for laser ablation effect, and the ablation energy can be reduced greatly by the process; the ablation efficiency can be higher with lower laser intense.