Determining the representative elementary volume (REV) of tight sandstone remains challenging because CT resolution and field of view impose competing constraints on pore-structure characterization. In this study, six tight sandstone samples were examined using multi-resolution micro-CT with voxel sizes of 0.556, 3.98, and 10.5 μm. A unified stability-index method was used to evaluate geometric, topological, and hydraulic parameters, including porosity, fractal dimension, anisotropy, pore-size distribution, specific surface area, coordination number, sphericity, tortuosity, and permeability. The results show that both CT resolution and field of view influence REV estimates. High-resolution images preserve more micropores, narrow throats, and irregular boundaries, whereas low-resolution images lose fine-pore information but better capture larger-scale structural heterogeneity. Hydraulic parameters generally require larger REVs. Porosity and coordination number show scale-dependent trends similar to those of the hydraulic parameters, indicating that pore-space abundance and network connectivity jointly influence the representative scale of flow. Pore-size distribution and anisotropy provide more reliable REV estimates at high resolution, while fractal dimension, specific surface area, and sphericity are more sensitive to changes in resolution. Therefore, flow-related REV evaluation in tight sandstone should account for resolution limitations and integrate multiple geometric, topological, and hydraulic parameters rather than relying solely on porosity.