Provided is a step sand-blocking dam ecosystem for reservoir desilting and sand prevention. According to topographical conditions, a reasonable position is selected, in the outer river segment of the upstream backwater area of the reservoir area, as a dam site where a sand-blocking dam is built. The dam site where the sand-blocking dam is built is leveled by areas. The lower filling bag dam body of the sand-blocking dam is built by segments and layers on a cleared and leveled river bed by adopting large reservoir desilting soil filling bag technology; the upper dam body of the sand-blocking dam is built by adopting gabion boxes. Ecological restoration and protection are conducted on the surface of the sand-blocking dam, and ecological restoration is conducted on rivers in the upstream and downstream areas of the sand-blocking dam. According to the step sand-blocking dam ecosystem for reservoir desilting and sand prevention, reservoir area desilting soil is used for building the dam and an ecological protection slope surface, so that not only is building cost reduced, but also ecological management and protection are combined into a whole by using local resources; water and soil loss in the reservoir area can be reduced, the ecological environment of the reservoir upstream area and surrounding areas is significantly improved. The step sand-blocking dam ecosystem for reservoir desilting and sand prevention is suitable for siltation prevention and treatment and ecological management work of reservoirs with heavy vegetation damage, ecological environment deterioration and heavy water and soil loss in large reservoir areas in central and western regions.