when the plant protection unmanned aerial vehicle (UAV) is used to spray pesticides on orchard, the distribution of rotor downwash airflow filed has significant influence on the spatial movement of the droplet and the adhesion and penetration of the droplet inside the canopy. Based on computational fluid dynamics (CFD) method, combined with RNG κ-ε turbulence model, porous model and sliding mesh technology, the rotor downwash airflow field of a six-rotor plant protection UAV in hover when spraying on orchard was simulated. The simulation was done in the constructed virtual orchard. The characteristics of the airflow field were analyzed in different hovering heights of the UAV, fruit growth stages and natural wind speeds. Verification experiments were carried out through measuring the downwash airflow velocity at marked points. The results showed that: 1) it no longer met the conditions for spraying of the plant protection UAV in hover when the natural wind speed was greater than 3 m/s due to the downwash airflow under the rotor submerged in the natural wind of the environment. 2) Natural wind destroyed the central symmetry of downwash airflow of the rotor, and airflow diffusion appeared along the downwind direction. With the increase of natural wind speed and hovering height, the backward lift distance increased. When the hovering height was 3 m, and the natural wind speed was 1 and 2 m/s, the trailing distance of the rotor under the airflow reached 1 and 2 m respectively; when the natural wind speed was 3 m/s, the trailing distance had been more than 2 m. Under the condition of natural wind speed of 2 m/s, and the hovering height was 3 and 3.5 m, the trailing distances of the rotor under the airflow were not much different, both were both 2 m, but the former was in contact with the target canopy layer, and the latter was not in contact; When the hovering height was 4 m, the trailing distance of airflow had exceeded 2 m. 3) Compared with the state of no natural wind, the velocity distribution at the nozzle was mainly affected by natural wind, but the effect of fruit growth stages was not significant. In addition, the vertical z-direction airflow played a leading role in the target transport of the droplets. The spray head should be installed near 0.2 m directly below the rotor to make the droplets to have large z-direction velocity. 4) After the hovering position of the UAV was adjusted in the upwind direction, the average velocity of the upper, middle and lower airflows in the canopy increased from 1.36, 0.80 m/s, and 0.81 to 3.04 m/s, 2.37 and 1.63 m/s, respectively. The coefficient of variation of velocity distribution in the upper and lower layers decreased from 74.26% and 35.80% to 45.39% and 22.70%, respectively, and the middle layer increased slightly, which was beneficial to achieve target spray. The experimental results showed that there was a good consistency between the experimental and simulated values of downwash airflow velocity at marked points. In conclusion, this paper should provide further reference for the development of the adaptive control technology of plant protection UAV hovering target spraying in a dynamic environment.