Objective: The arc fault of oil-immersed transformers may result in explosions and corresponding fire accidents, which severely affect the safe operation of the power system. However, arc fault tests cannot be conducted on a large scale due to their high cost, implementation difficulty, and low repeatability. As a result, numerical simulations have become an important research method. Various types of simulation methods are available, and the validity and applicability of their numerical results and underlying physical processes need to be examined. Methods: Taking a 500 kV transformer as an example, this study used LS-DYNA to compare the effectiveness of the TNT equivalent method, instantaneous gas injection method, and uniform gas injection method in terms of spatial and temporal characteristics of arc fault explosion load of oil-immersed transformer. Thereafter, the response characteristics and failure modes of the structure, along with the influence of complex internal structures on the propagation of pressure, were explored. Results: The research results indicated the following: (1) The simulations revealed that the uniform gas injection method could reproduce the process of gas production during arc faults and efficiently reflect the effect of arc fault duration, with the generated peak pressure and pressure gradient closely matching the experimental data. The instantaneous gas injection method and TNT equivalent method yielded higher loads and might overestimate the structural responses. However, they could be employed for examining weak points of transformer structures during explosions because of their simple implementation. The uniform gas injection method was suited for precise response analysis and ultimate pressure limit analysis of transformer structures, which required high accuracy.(2) The arc fault load presented a rapid attenuation characteristic in space and time, which enhanced its local effect on the structure. However, due to the spatial limitations of the transformer structure and the space occupation of internal components, the reflection and superposition of pressure waves prevented the pressure from monotonically attenuating in time and space after reaching its peak. The multi-peak characteristics of the internal explosion pressure waves intensified the impulse within the complex structure.(3) Under the considered conditions, plastic deformation of the structure occurred in the turret structure immediately adjacent to the failure location. Bending deformation arose in the tank wall near the failure area, and substantial stress concentration was observed at the corner of the tank. Under high-energy conditions, the possible failure locations were found in the local area near the arc failure and the stress concentration points at the corners. The overall bending deformation could absorb energy and expand the fluid volume within the structure, which allowed the structure to withstand explosion loads.(4) An anti-explosion balance design concept for transformers was proposed, in which different load models were used for preliminary design, balance design, and pressure-relief design. The three stages corresponded to the static pressure bearing condition, the typical fault condition, and the rare occurrence condition. Conclusions: The uniform gas injection method effectively describes the gas generation process of the arc fault, and the load characteristics agree well with the test results. The arc fault load decays rapidly in time and space. Moreover, the complex pressure propagation path inside the transformer will considerably affect the local load. Based on the load and response characteristics, the stepwise balanced design concept adopting different levels of working conditions can improve the anti-explosion performance and realize economic benefits by simply strengthening the structure.