The thermal stress effects of the fused silica irradiated by a millisecond–nanosecond (ms–ns) combined pulse laser are analysed. Numerical results are in good agreement with the experimental results. The results show that (1) different pulse delay and energy density affect the temperature change of the fused silica; (2) observing the axial stress, it is found that nanosecond laser will lead to new damage areas near the film under the condition of millisecond laser pre-irradiation and (3) stress exfoliation is found in the study of damage morphology.