To quantitatively assess how check dam construction alters runoff-sediment processes and erosion-deposition patterns in small watersheds, we established a physical watershed model and subjected it to controlled indoor rainfall simulations. Four consecutive rainfall events with intensities of 60, 90, 120, and 150 mm/h were applied, and surface topography before and after each event was captured using high-resolution three-dimensional laser scanning. The experiments aimed to elucidate the hydrological and geomorphological responses of the watershed. Runoff and sediment yield increased progressively with rainfall duration and then approached quasi-steady values with only minor fluctuations. Relative to the no-dam scenario, runoff in the dammed watershed decreased by 1.8-12.3%, while sediment yield was reduced by 22.72-42.44%. Under varying rainfall intensities, the nodam scenario model was dominated by severe erosion, exhibiting a soil loss volume of 0.0059 m3/m2and limited deposition 0.02 m3. In contrast, the presence of a check dam substantially mitigated main-channel incision and effectively constrained gully and bank erosion within the dam-controlled area, reducing soil loss to 0.0039 m3/m2and increasing total sediment deposition to 0.19 m3. The check dam elevated the local erosion base level, weakened flow energy, and promoted sediment retention upstream. Together, these results demonstrate that check dam construction markedly modifies the hydrological and geomorphic evolution of small watersheds under continuous rainfall, and they provide a process-based basis for optimizing dam design and sediment-management strategies on the Loess Plateau and in other erosion-prone regions.