[Objective] To address the insufficient lightweight and continuous three-dimensional expression of two-dimensional hydrodynamic outputs, an integrated method combining hydrodynamic calculation, 3D rendering, and risk mapping was established for urban waterlogging deduction. [Methods] Based on the results of drone oblique photography, a three-dimensional real scene base was constructed, and the MIKE FLOOD coupled model was established using MIKE URBAN and MIKE 21. And the model was calibrated using the actual rainfall process measured on April 25, 2022, and further validated with the typical rainstorm process on July 1, 2017. In the 3D dynamic simulation phase, the focus is on constructing a floating-point texture mapping method: converting the results output by the hydrodynamic model into temporal texture data according to a uniform grid index. The relative elevation of water surface is encoded using RFloat single-channel texture, while the flow velocity field is encoded using RGFloat dual-channel texture. Global min-max normalization is used to maintain consistent data scales at different times. In the 3D engine, UV mapping is established based on the coordinate transformation relationship between the model grid and the 3D scene. The elevation changes of water surface are driven by the Crest plugin, shader sampling, and frame interpolation. At the same time, information on water depth and flow velocity are extracted from the texture, the HR hazard index is calculated based on water depth-flow velocity combination, and dynamic heat maps are generated according to risk thresholds to achieve synchronized expression of urban flooding process display and pedestrian water risk assessment. [Results] Calibration results showed that the maximum absolute error of water depth at four typical waterlogging points was 0.12 m, and the average error was controlled within 0.10 m. The verification using the 2017 rainstorm event indicated that the simulated inundation distribution was generally consistent with historically reported flood-prone locations, including Yingxia Road, the Jinxia Garden area, and the Furong Road-Shengshi Road intersection. Under rainfall scenarios with return periods of 50, 100, and 200 years, the total inundated areas in the study area were 41.81, 45.06, and 47.61 hm², respectively, and the proportions of inundated area with water depths greater than 0.15 m all exceeded 70%. Under the transposed “7·20” extreme rainstorm scenario, the system loaded 397 frames of elevation and velocity textures, and the three-dimensional simulation maintained a stable frame rate of approximately 60 FPS. The system continuously displayed the waterlogging development process characterized by initial ponding in low-lying areas, expansion along road depressions, and subsequent connected inundation with increasing water depth. The HR-index-based risk heat maps showed that the risk levels along Furong North Road and near the Xiangjiang Road-Shengshi Road intersection gradually evolved from low risk to medium, high, and very high risk as the rainfall process developed. [Conclusions] This study establishes a loosely coupled technical route for converting MIKE FLOOD numerical simulation outputs into the Unity 3D real-time rendering environment. The main innovation lies in the proposed floating-point texture encoding method for hydrodynamic result conversion, which enables continuous three-dimensional expression of water depth, water-surface elevation, and velocity vectors. In addition, a dynamic risk mapping mechanism integrating hydrodynamic fields and the pedestrian hazard index was constructed, allowing urban waterlogging simulation results to be extended from static inundation display to process-oriented, interactive, and risk-oriented three-dimensional visualization.