The critical compressive strain calculation formulas widely adopted in international standards are primarily established based on bending test results, with insufficient consideration of the effects of other load forms such as axial compression on pipeline buckling behavior. To investigate the applicability of Code for Seismic Design of Oil and Gas Transmission Pipeline Engineering (GB/T 50470—2017) in calculating critical compressive strains under axial compression and bending loads, an analytical study was conducted through numerical simulations. Nonlinear finite element software was employed to establish numerical models, through which the buckling response characteristics of pipelines under the two load conditions were compared. The influences of different parameters on buckling were analyzed, and critical compressive strains under various conditions were contrasted with results calculated using the formula recommended in Code for Seismic Design of Oil and Gas Transmission Pipeline Engineering (GB/T 50470—2017). The results indicate that as internal pressure increases, the critical compressive strain of the axial compression model exhibits an upward trend, whereas that of the bending model first decreases and then increases. With the rise of diameter-to-thickness ratio and yield-to-tensile strength ratio, critical compressive strains of both axial compression and bending models decreases. While the Code for Seismic Design of Oil and Gas Transmission Pipeline Engineering (GB/T 50470—2017) results are conservative compared to the bending model, they are non-conservative for the axial compression model, revealing the unreliability of neglecting load characteristics in strain-based pipeline design. Based on simulation results, the practical influence of axial compression loads was incorporated into the assessment framework for pipeline buckling failure. A refined analytical formula with higher accuracy and appropriate conservatism was derived through regression analysis for calculating critical compressive strains. The findings provide essential theoretical foundations and technical support for the safe design and operation of pipeline engineering.