Abstract: In order to clarify the field sampling methods suitable for pesticide residue testing under the application mode of unmanned aerial spray system (UAS) for plant protection, this study explored the four sampling methods, Z-shaped method, checkerboard method, diagonal method, and '米'-shaped method, under optimal application conditions, and the density distribution of droplets under different sampling points, and evaluated the uncertainty introduced by the sampling methods. The results show that the optimal operating parameters of T30 plant protection UAS were: flight speed of 3 m/s, flight altitude of 2 m from crop canopy, and working distance of 5 m. The spray deposition content at the periphery of the spray operation area of the plant protection UAS has a great influence on the change of the average spray deposition content in the region, and the residual samples should be collected as much as possible to avoid collecting from the periphery of the application operation area. In order to increase the uniformity and representativeness of field sample collection in the application mode of plant protection UAS, it is recommended that the number of sampling points should be set at 18 or more, and the diagonal method, checkerboard method or Z-shaped method can be selected.