Abstract: Trajectories of water droplets were studied to provide information for anti-icing system design of inlet of an engine. Based on the calculation of flowfield around the inlet, numerical results of the motion equations for the droplets were presented by using difference method, and the droplet trajectories were obtained for a variety of flight conditions. Then, the impact range on the inlet surface, the total collection efficiency, and the local collection efficiency were determined. In addition, the effects of flight height, flight velocity, and radius of water droplet on droplet trajectories were also investigated. It was found that the impact range, the total collection efficiency and the local collection efficiency all increase with decreasing of flight velocity, increasing of droplet size or flight height. At the same time, the reasons of these results were analyzed.