In a device for producing quantitative-diameter spray droplets of pesticide, a driving motor is controlled by a control center, the driving motor drives a lead screw, the lead screw drives a sliding device to achieve a designated accurate position on a guide track, and a piston moves slowly along with the sliding device to extrude chemicals in a droplet generator quantitatively, the chemicals extruded by the piston through the motion in a droplet cavity forms small single droplets through a guide pipe, the droplets with specific particle size are further generated by precisely controlling the extrusion amount of the chemicals, so that the device can be widely used for studies about diffusion of the droplets evaporation property of the single droplets and the like tested by water-sensitive paper, as well as tests of the properties of the pesticide, and further has broad application prospects.