Aiming at the limitation that the single-factor model ignores the combined effect of internal pressure and internal fluid weight in the traditional submarine pipeline buckling theory, this study proposed a multi-factor joint analytical solution optimization method based on secondary buckling analysis. Firstly, by combining the Coulomb friction law, Maltby formula and Hobbs and Taylor buckling theory, an analytical model for the secondary buckling deformation of the pipeline under the combined action of temperature-internal pressure-internal fluid weight was established, and the analytical solution of the cap-shaped buckling mode was derived. Secondly, through the thermal-solid coupled finite element model, the pipe-soil contact stiffness and boundary condition parameters were calibrated with experimental data to ensure the equivalence between the numerical model and the actual working conditions. On this basis, the empirical coefficient K₁ in the analytical solution is corrected by comparing the theoretical solution with the simulation results, so that the error in the buckling displacement prediction is reduced to less than 2%. The results show that the contribution rate of the internal fluid weight to the axial compression of the pipeline is 35.89%, a factor that significantly affects the critical buckling threshold. The prediction accuracy of the modified analytical solution is improved to more than 98% under the combined condition. The results provide a high-precision theoretical tool for the anti-buckling design of deep-sea pipelines, and lay a methodological foundation for the stability analysis of pipelines under the combined action of multiple physical fields.