Abstract: Environmental DNA（eDNA） technology is a key tool for river health assessment. It shows great application potential in the biological analysis of aquatic ecosystems. However, the relationship between eDNA and sediments that are widely present in water bodies is complex, and eDNA is also affected by water flow, which seriously restricted the promotion and application of eDNA technology. Therefore, it is necessary to investigate the influence of sediment and water flow on the degradation of eDNA. This study took Ctengodon Idella, an important freshwater cultured fish in China, as the research object to explore the influence of water flow and sediment on the persistence of eDNA of grass carp. The results show that:（1） In flowing water bodies, the degradation rate of the eDNA accelerates with the increase of flow rate.（2）The presence of sediment accelerates the degradation rate of eDNA in water. Compared with the thickness of sediment laying, the sediment partical size has a greater impact on eDNA degradation.（3） Notably, in still water, the eDNA degradation rate decreases with the increase of sediment partical size. While in flowing water, water interference leads to the opposite eDNA degradation pattern, that is, the degradation rate of eDNA increases with the increase of sediment partical size. The study emphasizes that the impact of the sediment response method is critical in planning or interpreting eDNA studies and provides a valuable reference for the application of eDNA technology in aquatic ecosystems.