In order to evaluate the safety of a submerged structure subjected to UNDerwater EXplosion (UNDEX) loads, it is necessary to estimate the structural response accurately. This paper describes the interaction between surface pressure acting on a structure and the structural response of a submerged structure. Firstly, the detailed investigation of the interaction between surface pressure and the structural response for a 2-dimensional submerged structure using Fourier series analysis formulated by Huang, is presented. For the purpose of evaluating the fluid-structure interaction effect to the structural response, a new parameter FSI Ratio is proposed. Secondly, to simulate the structural response of a realistic 3-dimensional submerged structure, a 3-dimensional finite element analysis (FEA) code with the fluid-structure interaction model based on an approximation technique called the doubly asymptotic approximation (DAA) is developed. From the comparison of the numerical results using this developed code with the Fourier series analysis and the existing experimental results, the validity of the present algorithm is illustrated. And, it is also shown that the adoption of a double exponential function as a incident pressure waveform improves the accuracy of the FEA with the DAA fluid-structure interaction model.