Abstract: This study addresses the technical challenges associated with near-field shock wave measurement during large-depth underwater explosion tests conducted within explosive pressure vessels. A novel indirect measurement method is proposed, based on a straight-through cylindrical shock tube structure, specifically designed for near-field shock wave measurement in confined environments. This approach provides a new pathway for acquiring free-field shock wave parameters from underwater explosions, particularly offering critical insights for obtaining near-field free-field shock wave parameters under the demanding conditions of high-pressure confined environments. The core methodology involves the design of a straight-through shock tube-based measurement structure. Leveraging the inherent one-dimensional shock wave attenuation characteristics within this straight cylindrical tube configuration, the method effectively transforms the high-amplitude, high-frequency near-field shock wave captured at the tube entrance (proximal to the explosion source) into a measurable low-amplitude, low-frequency shock wave at the tube terminus. This transformation significantly reduces the experimental difficulties inherent in direct near-field measurement. Furthermore, by utilizing multiple reflections of the shock wave off the inner walls of the straight shock tube, the method successfully increases the initial temporal phase difference between the subsequent reflected waves propagating within the pressure vessel chamber and the direct wave. This enhanced temporal separation enables the decoupled measurement of free-field overpressure within the high-pressure confined environment. Building upon the design principles of this straight-through shock tube measurement structure, the shock wave parameter inversion method is rigorously derived using dimensional analysis. Subsequently, the key parameter design methodologies for this specific measurement structure are presented. To validate the reliability of both the measurement and inversion techniques, shock wave measurement experiments were conducted using small-equivalent explosives in an explosion pressure vessel. The experimental results provide effective verification of the proposed approach. The work presented in this study offers a low-cost and highly feasible practical complement to the techniques available for near-field shock wave measurement in underwater explosions conducted within high-pressure confined environments.