To define different effects of several concentrations pesticide for pest prevention under air assisted spraying condition, pest population decline rate and disease index were used to test effects of two kinds pesticide which were applied to pear aphids and pear black spot. Furthermore, the droplets distribution inside the canopy was also analyzed with Brilliant sulfaflavine, and the reasonable range of pesticide concentration for air-assisted spraying application was proposed. The results showed that: the amount of pesticide was 0.24L per tree, which was decreased by 33.3% compared to artificial spraying under the condition that the sprayer speed was 1m/s, the rotary speed of fan was 1200r/min, and the wind flow was 7.2L/min in one side. Compared to artificial spraying, air-assisted spraying application can achieve better control effect with the same quality of pesticides. The distribution of droplets under air-assisted condition was better than traditional way, and the amount of pesticide was suggested 1/3 that of artificial spraying, at the same time, the concentration could be increased properly in order to reach better effect, and the actual pesticide mass was suggested 1/3～1/2 that of artificial spraying.