Power transformers are inevitably subjected to short-circuit (SC) faults in operation. Verifying the SC resistance is an important means to evaluate their operation stability. A 110kV power transformer failed due to insufficient SC capability was chosen in this paper, a refined model for SC resistance verification is established by FEM. It precisely calculations the axial and radial leakage magnetic field distribution and forces distribution of transformer windings under different operating conditions. Results are compared with the disassembly inspection and forces distribution calculation. Results shows that the refined verification results of the transformer are consistent with the actual instability phenomenon. Specifically, the maximum axial compressive force at the winding end fails to meet the allowable value, and a corresponding inclined collapse occurs at the winding end. This method provides robust support for optimizing transformer short-circuit resistance design and enhancing fault analysis.