This paper analyzes the causes of siltation in the Old Course of the Fuhe River based on the sandbar evolution, water and sediment inflow conditions, and the impacts of siltation by the sandbar vegetation. It was found that from 1985 to 2022, the area of sandbars in upstream of the Old Course of the Fuhe River continued to grow and the main channel silted up. The sandbar vegetation in the upstream grows luxuriantly. Under the influence of water blockage by floodplain vegetation, the flow velocity decreases, and the sediment concentration decays along the reaches, which promotes sediment deposition in the upper reaches. After the incoming water and sediment of the upper reaches enter the middle and downstream reaches, the average flow velocity decreases along the reaches due to the widening of the section width, resulting in sediment deposition. Moreover, The diversion water volume of the old course of the Fuhe River shows a decreasing trend year by year. The water and sediment conditions in the Old Course of the Fuhe River are suboptimal. During periods of low flow, siltation occurs frequently, and during high-flow events, the river lacks sufficient power to flush away the sediment deposited during low-flow periods. This dynamic results in a continuous accumulation of sediment within the channel. Based on a two-dimensional mathematical model, we designed multiple water-sediment control scenarios, incorporating various sandbar structures and vegetation distributions. Through detailed calculations and analyses, we proposed the following countermeasures: When the sediment concentration at the inlet of the Fuhe River exceeds 0.01 kg/m3, introducing controlled high-flow events with flow rates maintained between 85 and 125 m3/s can effectively transform the upstream section from a state of siltation to scouring. In the middle and downstream reaches, applying sandbars-cutting techniques and adjusting vegetation distribution can enhance the sediment transport capacity, thereby slowing down the rate of siltation in these areas. These countermeasures aim to provide a valuable reference for similar small and medium-sized rivers, improving their siltation conditions and restoring and maintaining the health and stability of river ecosystems.