Abstract: This paper carries out numerical simulation calculations of steel pipe under joint action of internal strength and bending loads using finite element method (FEM). By means of analysis on the influential factors of critical buckling strain, it determines calculating working conditions, constructs a finite element model, studies the impact of diameter/thickness ratio, internal strength and steel grade on critical buckling strain, and according to numerical calculation results, obtains nonlinear coefficient through Matlab regression to establish a critical buckling strain calculating formula of line pipes under the action of internal strength and buckling loads by regression. The physical test results verify that the established calculating formula has the higher prediction accuracy, if compared with CSA/DNV calculating formulas.