A pulse width modulation (PWM) variable spraying system based on miniature unmanned aerial vehicle was developed, and based on controllable multi-speed environment, a droplet deposition test through droplets concentration method was studied for the PWM spraying system when the UAV was hovering. The system is consisted of airborne spraying device and ground measurement and control unit. The airborne spraying device with the MCU of STM32F103VC was remotely controlled by the ground measurement and control unit which was developed by LabWindows/CVI through wireless data transmission module. Frequency of 10Hz square wave and adjustable duty ratio were evaluated to control micro electric diaphragm pump, and then pressure and flow rate of the system were changed. The experiments were carried on under the condition of different distance and wind speed to get the relationship among deposition volume, duty ratio, nozzle type, and the rotate speed of centrifugal nozzle. The results showed that wind speed was the most significant factor influencing the droplet deposition. Deposition volume was distributed in a parabolic type in the collection area, gradually decreased and the deposition peak was far away from the nozzle with increasing of wind speed. Droplet diameter was not very important to deposition when wind speed was smaller than 3m/s. When the wind speed was greater or equal to 3m/s, the droplet was drifted of different diameters, and the deposition volume reduced significantly and moved away from the nozzle. Small droplet size (101.74μm) was much easier to be drifted, and the peak concentration was 4m far from the nozzle. Also the deposition volume of small droplet size was much lower than droplet size of 164.00μm and 228.16μm. The optimization of spraying parameters and a theoretical support to improve the quality of aviation operations were provided by the results.