To study the damage characteristics of simply supported steel box girder bridges under near-field explosive loading, software LS-DYNA was used to establish the finite element model. Numerical validation was carried out for the steel box girder scale model, and the reliability of the numerical simulation method was verified. Damage simulation was carried out to explore the damage characteristics of the steel box girder bridge with different explosion loading cases and locations. The results show mainly local damage of simply supported steel box girder bridge under near-field explosive loading, and is mainly manifested as top plate failure, bottom plate failure and partitions deformation and failure. The top plate is the most serious failureis, which is affected by the direct impact of the explosion loading. The explosion location exerts a dominant effect on the failure of the bridge, and the failure area of the top plate at the location without diaphragm restraint is increased by 50%−70% compared with that at the location with single or both transverse and longitudinal diaphragm. Moreover, the stiffening ribs on the longitudinal diaphragm will reflect the shock wave, result in shift of the bottom plate crack. The maximum crack center shift is 0.5−1.5 m in 500 kg with the increase of TNT equivalent. Therefore, the protective effect of the diaphragm and the stiffening ribs is criticle for steel box grider bridges design.