Abstract: Above-deck explosion accidents occur frequently in recent years, while the existing studies concerning the blast resistance of bridge mostly focus on the failure mode and damage assessment of a single reinforced concrete (RC) bridge pier instead of the damage assessment of the deck which guarantees the bridge transportation capacity. At present, the residual bearing capacity of a bridge deck is adopted as the damage index to numerically and quantitatively assess the damage levels of the prestressed RC T-girder bridge under above-deck explosions. Firstly, based on the above-deck explosion test on the prestressed RC T-girder bridge and static bearing capacity test on the full-scale prestressed RC T girder, the applicability of the adopted finite element (FE) analysis method in explosion and static bearing capacity scenarios was verified by comparing with the experimental reflected overpressure-time histories, failure modes, acceleration-time histories of deck and static bearing capacity of T girder. Next, the refined FE model of a prototype T-girder bridge was established. Then, the dynamic behavior of the prototype bridge under explosion of the seven threats specified by Federal Emergency Management Agency (FEMA) was analyzed by the validated FE analysis approach. The results show that: the damage modes of the entire bridge caused by seven threats from the pipe (2.3 kg TNT) to the passenger van (1814 kg TNT) bombs in order include the plastic state of the concrete of the deck, T girder and diaphragm, opening in the deck, and breaching of the T girder, diaphragm, deck and supporting substructures. Afterwards, the damage index based on the residual capacity of deck was defined, and the corresponding values of the deck under explosion of different threats were given quantitatively, e.g., the damage index value range of deck under explosion of the pipe (2.3 kg TNT), belt (4.5 kg TNT) and vest (9.0 kg TNT) bombs is 0.01-0.06, and the entire bridge remains intact, while that of the compact sedan (227 kg TNT) and sedan (454 kg TNT) bombs are 0.84 and 0.96, and the entire bridge loses bearing capacity totally.