In an effort to investigate the influence of downwash airflow field on droplet motion characteristics of small unmanned aerial vehicles (UAVs) and enhance pesticide application efficiency, small UAVs were utilized as the basis and the Navier-Stokes (N-S) equations, realizable k-ε model, and Semi-Implicit Method for Pressure-Linked Equations algorithm were employed to detailed numerical simulations of the downwash airflow field and droplet dispersion motion during the spray process were carried out. The primary research focus encompassed the analysis of velocity characteristics of the UAV downwash airflow, droplet deposition characteristics, and the impact of operating height on pesticide deposition. By comparing simulated values with measured values, it was confirmed that the relative error between the simulation and the experiment remained within 20%, thereby verifying the feasibility of the downwash airflow field numerical model. Further simulation analysis results indicated that, under the influence of the UAV spray platform, the downwash airflow field attained its peak velocity at a distance of 1 m from the rotor. With the increase in operating height, the droplets gradually dispersed and diffused. The droplets were primarily distributed in two “airflow introduction zones” and two “airflow export zones”, which contributed to further optimization of spraying effects and enhanced efficiency of pesticide utilization. In light of the analysis results, it was substantiated that when the UAV flight operation attitude was kept flush with the ground and the operating height was adjusted to 0.8~1.0m, pesticide deposition could be significantly increased, ultimately improving the pesticide application efficacy of plant protection UAVs. The research result verified the feasibility of the numerical model of downwash airflow field, and provided a reference for the study of the drift and deposition of target fog droplets based on small plant protection UAVs.