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Plant protection drone has great application prospects in agricultural production due to its low working height, flexible operation, good adaptability to terrain, slight environmental pollution and high efficiency in pest control. However, it could cause secondary disasters with droplets drift due to wingtip vortices. To investigate the effect of wing tip vortex flow of a single-rotor unmanned aerial vehicle on droplet drift, the flow field under a singlerotor unmanned aerial vehicle (UAV) was simulated numerically based on an adaptive thinned physical model of the lattice-Boltzman (LBM) method. The drift characteristics at different flight speeds of the wingtip vortex were examined for various nozzle positions and vertical distances between different spray booms. The Lagrange discrete particle tracking method was applied to capture accurately the trajectories of droplets with different particle diameters. Spray tests were conducted to verify the accuracy of the numerical simulation. It was shown that as the UAV flight speed was greater than 3m/s, a spiral tail vortex appeared at the rear of the fuselage. The range of the tail vortex behind the fuselage became longer as the flight speed or flight altitude got higher. And 38% of the droplets was drifted by the spiral tail vortex at the flight speed of 5m/s and the flight height of 3m, in which 80% of the drifted droplets was smaller than 100μm. The distance between the sprayer and the main rotor had little effect on the drop drift caused by the wingtip vortex. While the nozzle was closer to the edge of the main rotor, the droplets can be more easily sucked by the wingtip vortex.