In order to effectively cover target weeds, improve the precision of target spray and reduce liquid pesticide waste and ecological pollution, the target spray method based on two-degree-of-freedom manipulator was adopted to optimize the target spray performance of the weeding robot. The establishment of the liquid pesticide spray model of weeding robot was the key to improve the precision of the target spray. Under the premise of considering the wind disturbance, according to the dynamics equation of the droplet particle trajectory, combined with the manipulator link and the joint variable parameters, the model of droplet spray was established and the theoretical covering area was derived. Based on this, the influence of nozzle pose, vehicle velocity and wind speed on the covering area of liquid pesticide droplet was analyzed by computer numerical simulation, and coordinate reconstruction was carried out on the nozzle spray point. A small opening direct-current low-speed wind tunnel was built indoors and the liquid pesticide spray model validation tests were conducted. The actual droplet covering area was obtained by image processing technology, which was compared with the theoretical droplet covering area, the area centroid error range was 4.1~7.2mm, and the area matching error range was 9.1%~17.8%. The experimental results showed that the error of the theoretical covering area compared with the measured test results was small and had a high consistency with the test results. This research can be used as a reference for the construction to target spray equipment and technology of related robots.