In order to study the effect on air flow rate of air-assisted and the distance of air outlet to nozzle to the droplet diameter and droplet velocity,the air-assist boom spray field was tested and analyzed in various conditions using PDPA measurement system. According to the test results, the droplet diameter distributions, velocity distributions and the relationship between air pressure and droplet diameter were analyzed systematically. The test results indicate that under the influences of flow field,the higher the air flow rate of air-assisted is, the smaller the droplet diameter is,increasing the droplet deposition,reducing the droplet drift.And its distributions are more symmetrical.The closer distance between the air outlet to the nozzle,the better droplet penetration is,reducing the trend of droplet drift.