In order to further clarify the damage characteristics of steel square pipe under localized lateral explosion.Using the finite element software LS-DYNA and the method of fluid-solid coupling and adding mass damping,distinguishing different burst distances within 10~20 cm,the impact of 160 g cylindrical explosives on a steel square tube with a cross-sectional area of 13.51 cm2 was studied.Analyzing the theoretical calculation value and numerical simulation value of the ultimate bearing capacity of steel square pipe,it is found that the difference between the theoretical calculation value and the numerical simulation value is 2.63%.Analyzing the experimental displacement value and numerical simulation displacement value of the center point of the explosion face of the steel square pipe,it is found that the errors are within a reasonable range,indicating that the model built is reasonable and credible.Analyzing the axial residual bearing capacity of the steel square pipe,it is found that with the increase of the burst distance,the axial residual bearing capacity of the square pipe increases in turn.Analyzing the energy absorption capacity of the pipe under the explosion load,it is found that the typical damage mode of the steel square pipe is that the central area of the explosion facing surface is obviously concave,and the steel pipe has no obvious deformation as a whole.The damage index,radial indent index and radial removal index were defined,it is found that the radial indentation index curve determines the overall change trend of the damage index curve,and the radial displacement index curve affects the local curvature of the damage index curve.The engineering algorithm for damage index of axial bearing capacity is proposed by fitting damage index.