Abstract: In this paper, the deformation and failure of a cylinder with inner pressure, which is irradiated by high power continuous wave laser beam, are investigated using the similarity analysis theory and FEM. At first, several dimensionless parameters are presented as the similarity criterion based on the dimensional analysis and equations analysis methods. In order to verify the above criterion, numerical simulations on mechanical responses of different size cylinder, but with the same similarity parameters, are accomplished with the commercial FEM code ANSYS. FEM results demonstrate that main dimensionless physical parameters are invariable at the same dimensionless position and time in different scale models, and prove that the similarity criterion presented in this paper is valid.