[Objective] Existing underwater search-and-rescue (USAR) platforms typically focus on general underwater tasks, but lack the ability to reproduce flood-typical hydrodynamic features, such as high turbidity, layered currents, debris-induced disturbances, and breach-driven scouring. To address this critical gap, this study aims to design, construct, and experimentally validate a modular underwater rescue simulation device capable of replicating the characteristic hydrodynamic and operational conditions encountered during dam breaches, dyke failures, submerged-structure collapse, and flood-area victim search. The objectives are fourfold: (1) develop a structurally stable, transportable, and reconfigurable test chamber featuring multi-functional side-panels for various rescue scenarios; (2) establish hydrodynamics-consistent testing conditions for visual recognition, acoustic localization, cutting, salvage, and structural operation tasks; (3) verify the dynamic and static performance of the system to ensure safety and fatigue resistance under flood-like loads; and (4) demonstrate the device’s effectiveness through field trials in a natural river environment exhibiting real flood characteristics. [Methods] A modular rectangular device-comparable in size to a standard 10-ft container-was designed using high-strength steel frames and detachable 10-mm marine-grade steel side-panels. These interchangeable panels integrate recessed cube targets for visual localization, transparent observation domes, knock-induced acoustic sources, and functional interfaces for cutting and salvage tasks. The modular architecture allows multiple units to be combined into large, connected test spaces, thereby supporting multi-equipment cooperative operations. Structural validation included modal analysis, static strength analysis, and safety-factor evaluation. [Results] Modal analysis produced natural frequencies of 157.9, 162.1, 230.0 Hz, and 249.9 Hz-values significantly higher than all typical operational excitation bands (0.5-20 Hz). This demonstrates robust dynamic stability and minimal resonance risk. Static strength evaluation revealed a maximum stress of 1.23×10⁸ N/m², far below the steel yield strength (3.50×10⁸ N/m²), and a maximum displacement of 12.4 mm, satisfying the GB 50017—2017 deformation limit of L/250 (12.8 mm). The safety factor reached 2.84, surpassing the CCS requirement of 2.0, confirming ample structural safety margins. Field experiments demonstrated that under extremely low-visibility (turbidity >100 NTU) and strong-current (1.2-1.4 m/s) conditions, rescue robots maintained reliable operation. Average visual target recognition distance reached 2.1-3.3 m; acoustic source localization errors were as low as 0.26-0.38 m. In dyke-breach simulations, robots successfully executed hooking, inspection, and cutting tasks with an 83% success rate in high-current zones, increasing to 95% in quieter sections. Across 12 joint-operation trials involving different rescue platforms, the device provided 100% stable operational space, and robots maintained posture errors below 3.2°, enabling high-precision maneuvering in confined environments. Overall task completion rate reached 89%, validating the realism and applicability of the simulated flood scenarios. [Conclusions] This study presents a fully validated, flood-condition-oriented underwater rescue simulation device that fills a long-standing technological gap in emergency rescue testing. Its key innovations include: (1) a modular, reconfigurable architecture enabling rapid construction of diverse flood-scenario environments; (2) high-fidelity reproduction of flood-typical hydrodynamics, including high turbidity, layered high-velocity currents, and confined operational spaces; (3) an integrated acoustic-visual multifunction test ecosystem supporting full-chain rescue tasks; and (4) proven engineering-grade structural stability ensuring safe deployment in real river environments. Results from field trials show that the device reliably supports multi-platform rescue operations and enables quantitative evaluation of underwater detection, localization, manipulation, and structural operations under extreme conditions.