In order to study the vertical distribution of spray droplet deposition of plant protection multi rotor UAV in low altitude spraying operation process, droplet test card were placed in rice canopy leaves, middle leaves and bottom leaves to collect protection UAV spray droplet. Water was used instead of pesticide in spraying process simulation, and iDAS analysis software was used to analyze the droplet deposition on the test card and the distribution of spray droplet deposition at different positions. The results showed that the spray droplet coverage rate of low altitude UAV in vertical direction was significantly different, the droplet coverage effect in the effective range and below rotor was the best, and the droplet coverage effect away from the rotor was poor. From different positions of rice canopy, overall droplet coverage rate in canopy was 54.86%, in middle canopy was 32.69%, and in bottom canopy was 24.7%. The particle size distribution in the vertical position of rice was in the range of 110~140μm, and the particle size was suitable for the prevention and control of plant diseases and insect pests. The density of the canopy was the highest, while the density distribution of the middle part and the bottom of rice was similar. The central rice droplet diffusion ratio (0.465) was better than those of the canopy (0.38) and bottom (0.31), the overall spray width and relative numerical diffusion of particle spectrum were lower than the normal value (0.67).