In order to solve the problem that the accuracy of plant protection machinery in the process of target application in large fields is reduced due to the drift of fog droplet deposition, a research on the method of fog droplet directional deposition control was carried out based on the robot of target application in large fields. Based on the target spraying droplet population, the working principle and operational characteristics of target application were explained, and the causes of droplet population deposition shift were analyzed. Combined with the prescription chart target position information to control the nozzle for fast action, the target spraying simulation test was carried out on a leveled field with target spraying accuracy and deposition offset distance as test factors, and the group meeting the operational requirements was selected for the verification of target application in a large field. The test results showed that the average accuracy of target application on level ground at 0.5m/s, 1.0m/s, 1.5m/sand 2.0m/s was 99.8%, 98.4%, 95.9% and 76.5%, respectively, and the deposition offset distance was 3.8cm,5.4cm, 7.5cm and 10.0cm, respectively. The fieldtotarget application accuracies of the operating speeds were 98.7%, 96.7%, and 95.3% at speeds of 0.5m/s, 1.0m/s and 1.5m/s, respectively. The results showed that the nozzle control method based on GNSS/IMU Kalman filter for droplet deposition position prediction can meet the demand of target application in large fields. This target application simulation method allowed accurate recording of target application accuracy and droplet deposition offset distances in a near natural environment.