A failure experiment of internally pressured cylinder shell under laser irradiation is presented in Ref. [1]. To research the failure phenomenon, a thermo –elastoplastic numerical model is established in this paper. In this model, a heat conduction analysis coupled with strain rate is applied and factors such as the physical properties of material changing with the temperature and the pre-loading of the internal pressure are considered. The sub-structure method applied in this paper successfully confines the coupled heat conduction analysis and thermo –elastoplastic analysis in a much smaller range. The numerical results tally with those of Ref. [1]. It shows that the numerical model can describe the whole process of the thermal softening failure fairly well.