To evaluate the water quality of the Yellow River under the water-sediment regulation scheme (WSRS) prior to seasonal flooding in 2023, river water was sampled and monitored at the sections of Downstream Xiaolangdi Reservoir, Huayuankou, Jiahetan, and Gaocun, typical sites for monitoring the Yellow River’s water quality. The evaluation results reveal overall excellence in water quality from Downstream Xiaolangdi Reservoir to Gaocun, with all monitoring factors meeting the standards for Classes I, II, and III water quality, except for a temporary decrease in dissolved oxygen (DO) when suspended sediment was discharged from high-turbidity water. Notably, there is a correlation between the concentration of water quality factors and that of suspended sediment: higher suspended sediment concentration (SSC) at different times corresponds to elevated levels of chemical oxygen demand (COD), ammonia nitrogen (NH3–N), permanganate index (CODmn), five-day biochemical oxygen demand (BOD5), total phosphorus (TP), and manganese at the same section. On the contrary, lower SSC leads to a decrease in the pH and DO levels. No significant difference was made to the Yellow River’s water quality along the lower reaches of Xiaolangdi Reservoir under the WSRS, with the impact diminishing from upstream to downstream across the monitoring sections. Overall, the study findings objectively assess the pattern of changes in the Yellow River’s water ecosystem under the WSRS before seasonal flooding, providing crucial technical insights into how the Yellow River basin can be preserved and restored.