In view of the problem that it is difficult for highgap plant protection machines to enter the field in the middle and late period of maize, and the poor penetration of droplets by traditional plant protection UAV makes it difficult to prevent and control pests and diseases, combining the thermal atomization and low-volume spraying technology of pulse smoke machine with high-efficiency plant protection UAV, a plant protection operation scheme of UAV equipped with thermal fog spraying system was proposed. The thermal spray pipeline and remote control system were designed, and the spraying operation experiment of maize plant protection during grain filling period was carried out. Spraying operations were carried out with water instead of pesticides. Horizontal and vertical sampling points were set up in the test area. Droplets deposited at each sampling point were collected by water-sensitive test paper, and the deposition distribution results of thermal fog plant protection UAV droplets in different sampling areas were measured by the droplet analysis software. The results showed that there were obvious differences in droplet size and droplet density distribution in the spray area from -2m to 6m, and the droplets were more concentrated at the horizontal position of 0~2m from the nozzle. The droplet size and density from the corn canopy to the bottom layer in the vertical direction was decreased in turn, and the droplet density in the whole sampling area exceeded 20cm-2. The droplet coverage and deposition parameters were consistent with the overall trend. The droplet coverage rate of each vertical sampling layer at 1m from the front of the nozzle was the maximum, which was 18.02%, 13.48%, 4.37% and 2.11% from the corn canopy to the bottom layer, respectively. The droplet deposition amount on the front of leaves in the canopy also reached the maximum value of 0.36μL/cm2 in this area. In the whole, the droplet coverage rate and droplet deposition amount on the front of leaves were higher than those on the opposite side of leaves at the same position. In addition, except for a few sampling points where the droplet spectrum width was higher than 2μm due to droplet overlap and adhesion, the data of other sampling points met the technical index of droplet spectrum width less than 2.0μm under low-volume spraying conditions. The research result can provide a reference for the parameter optimization and correct use of the thermal fog plant protection UAV in the middle and late plant protection operations of high-stalk crops such as corn. The research can provide a reference for the parameter optimization and correct use of thermal fog plant protection UAV in the middle and late stage of plant protection operation of maize and other high stalk crops.