The shock load of underwater explosion usually includes shock wave load and bubble pulsation load. The structural damage caused by shock wave and bubble load is always a hot topic in ship design. It is generally believed that the impact of shock wave load on the structure is mainly local damage, while the impact of bubble pulsation load on the structure is mainly global damage. The actual damage process of underwater explosion load is often the result of the joint action of the two kinds of loads. However, it is difficult to quantify the contribution of the two kinds of elements to ship damage. In order to study the damage effects of two kinds of loads on ships, a variable section box girder was used to simulate the surface ship structure, and its response process under the impact of underwater explosion was experimentally studied. Both the influence of distance on shock wave and the conditions for utilizing bubble energy were considered in the design of the experiment. The results show that plastic hinge was formed in the box beam structure near water surface under the action of near-field explosion load, and the energy transferred by explosion load to the beam structure was mainly converted into the deformation energy of the plastic hinge. In addition, the dynamic strain response of the structure gradually decreased from the middle to the end of the box beam, and the residual plastic deformation mainly occurred near the middle of the structure. The continuous large opening mode on the upper surface of the box beam resulted in larger plastic deformation of the deck side plate and the upper part than that at the bottom of the hull.