The invention provides a scour prevention quantitative water intake for a rotary cover of a farmland low-pressure water delivery pipeline, and belongs to the technical field of farmland pipeline water delivery irrigation engineering. The scour prevention quantitative water intake comprises the low-pressure water delivery pipeline, and is characterized by further comprising a water inlet area, a water outlet area and a scour prevention device, wherein the scour prevention device is arranged in the water outlet area, the water inlet area is respectively connected with the low-pressure water delivery pipeline and the scour prevention device, the water inlet area is formed by connecting vertical pipes and a reducer tee which is installed on branches of the low-pressure water delivery pipeline, the scour prevention device is formed by the rotary cover and cylindrical connecting bases, a threaded rod is arranged in the middle of the cover top on the inner side of the rotary cover, the connecting bases are arranged on the vertical pipes in a sleeved mode and connected to the vertical pipes, a threaded mounting base matched with the threaded rod is arranged in the centers of the connecting bases, the rotary cover is in threaded connection with the connecting bases through the threaded rod and the threaded mounting base, and a locating pin preventing the threaded rod from sliding out of the threaded mounting base is arranged at the bottom of the threaded rod. Through the design of the rotary cover and the threaded rod, compared with other pressing plate type water intake, the scour prevention quantitative water intake has the advantages of being good in water stopping effect, reasonable in structure, stable in water flow and remarkable in backflushing effect.