Abstract:  By analyzing the dynamic reaction force of water flow，the motion differential equation of the rotary watering sprinkler is established. The critical ejection angle and the critical flow velocity are determined，and it is proved that the unique steady motion of the system is asymptotically stable in a wide range. On this basis，the shape and the irrigation area of the sprinkler are given. Finally，the influence of periodic water flow pulsation is discussed.

Key words: rotary watering sprinkler, steady motion, stability, irrigation area