Abstract: Abstract: Pests and plant diseases cause damage at different levels to China's grain production and economic crops every year. The annual area damaged by pests and diseases is about 470 000 000 hm2, resulting in significant yield losses-about 20% of the total grain yield. A small-size unmanned helicopter has the advantages of flexible operation, strong automatic control ability, and less droplet drift. In addition, pesticides it sprays can penetrate a crop canopy assisted by rotor airflow. Hence, the agricultural chemical control for pests and diseases in medium and small sized fields using a small-size unmanned helicopter is an important means to guarantee grain production. It is one of effective methods for Chinese pesticide-spraying mechanization.In order to realize the low-altitude, low-volume, and high-efficiency spraying demand of an unmanned aerial vehicle (UAV), its spray system, which is the key UAV part, must meet the requirements of lightweight, low-volume spraying and uniform spray. Based on the domestic and foreign UAV nebulization technology of agricultural chemical spray nozzles, we tested the performance of rotary hydraulic atomizers, which combined the advantages of both centrifuge atomization and liquid atomization, in this study. A comprehensive performance test system of nozzle atomization was applied to detect the effect of important factors including structure parameters (nozzle diameter), spray parameters (spray flow rate and pressure), and operating parameters (rotational speed) on nozzle atomization efficiency (droplet size), deposition distribution, and spray span. We analyzed the correlation between spray parameters and pump power consumption. Combined with the effect of motor voltage on motor power, the optimum nozzle working parameters were selected. The results showed that the voltage of a nozzle rotary motor had a more significant effect on droplet diameter than nozzle diameter and spray pressure parameters did. Along with the increase of motor voltage, droplets became smaller, giving a better atomization effect. Motor voltage also notably influenced spray span. The more the voltage was, the bigger the spray angle was, and the larger the span became. Droplet deposition presented normal distribution in the spray range. The best working parameters (10 V of motor voltage; 0.35 MPa of spray pressure; 0.7 mm of nozzle diameter) for UAV rotary hydraulic atomizers were determined by the comprehensive test results. When these parameters were applied, the pump power consumption rate was lowest, the average droplet size was 112.35 μm, the spray span was 3.88 m, and the motor power consumption was 8.6 W. The nozzle atomization performance test system adopted in the present study has been calibrated and analyzed for error in other literature. Its experimental system error displayed was less than 1%, so the test results obtained through this platform are reliable.The results shown here provide a theoretical basis and technical support for the mounting of this novel UAV spray device-the rotary hydraulic atomizing nozzle-onto an UAV to perform relative experiments to improve UAV operating quality and spraying efficiency in the future.