Abstract: Focusing on the challenges in understanding the structural safety evolution and failure criteria of a 100,000 m3; external floating roof storage tank under pool fire loads, a nonlinear finite element analysis model based on transient thermo-structural coupling is established. An improved multi-layer solid radiation model is employed to simulate the flame thermal load. Numerical simulations of the tank under fire are conducted on the ANSYS Workbench platform for various filling ratios, with a focus on the impact of temperature-dependent material degradation on structural load-bearing capacity. The study reveals that an empty tank undergoes global heating after fire exposure, with the upper-middle wall panels reaching a maximum temperature of 541.68 ℃. Failure occurs due to thermal buckling, leading to significant local deformation, and the failure time, determined based on the Third Strength Theory, is 1388.2 s. In contrast, a fully loaded tank exhibits a stratified temperature distribution influenced by the thermal sink effect of the crude oil. Due to the superposition of hydrostatic pressure and local thermal stress, the fire-exposed wall panel fails prematurely at 40.6 s. The research concludes that empty and fully loaded tanks follow distinct failure mechanisms, characterized by “thermal degradation” and “load superposition,” respectively. It is recommended to adopt the Third Strength Theory as a conservative safety criterion in engineering assessments. This study provides data to support fire early warning and differentiated firefighting cooling strategies for large-scale storage terminals.