Abstract: In order to research the damage effect of steel box under internal blast loading, experiments were carried out to explore the damage of steel box under different TNT charge masses. The common four-compartment steel boxes were used as research objects. By changing TNT charge masses, different damage modes and damage characteristics were observed. The results show that steel box damage level increases as the charge mass increases under the internal blast loading, the steel plate on the roof of the fully enclosed compartment gradually increases from a slight uplift to a crack at the end of the reinforcement, the failure mode gradually increases from slight deformation of inner diaphragm and the steel plate of the roof cover to obvious deformation and the increase of one side uplift of the free passage, and cracks at the reinforced part of the roof and fracture of the top of inner diaphragm are formed at last.