Sandwich panel is commonly used in ship and marine engineering equipment, such as side structure and superstructure deck of a ship, which is of good anti-explosion performance. This paper addresses a study on the dynamic response of the U-typed sandwich panel under explosion load through the numerical simulation and theoretical methods. Based on the orthotropic plate theory, the U-typed sandwich panel is simplified and transformed into a single degree of freedom (SDOF) spring system, the equivalent motion equation of the SDOF system and the expression of triangular explosion load function are established based on the SDOF theory, and the maximum response spectrum of the SDOF system is obtained. Then, the response of the equivalent SDOF system of the U-typed sandwich panel under explosion load is analyzed, and the theoretical results match well with the numerical simulation results, which verifies the accuracy of the theoretical method proposed in this paper. The theoretical method proposed in this paper could have good engineering applications for the structural anti-explosion design, and provide a reference for the evaluation of the anti-explosion performance of ship and offshore platform structures.