Spraying insecticide is a common practice in the control against pest insects. However, little attention has been paid to the biocidal radius of droplets. Therefore, in this study, we investigated the biocidal radiuses of abamectin, thiamethoxam and sulfoxaflor droplets controlling against wheat aphid (Sitobion avenae). The mortality of S. avenae showed a droplet density dependent process that can be described by an exponential model. Calculated mortality limit (A2) varied with the concentration of insecticides. Although similar LD50 values were observed in abamectin (13.77 ng aphid-1) and sulfoxaflor (14.52 ng aphid-1) against S. avenae, sulfoxaflor had a larger biocidal radius (r50) than abamectin due to its translocation ability at the same concentration. And sulfoxaflor had a relatively larger biocidal radius than thiamethoxam (LD50 = 68.42 ng aphid-1) because it is more toxic to S. avenae. The ratio of r50/VMD was introduced to estimate the potential of droplets. Droplets generated by the air atomizing nozzle (VMD = 43 μm) had higher value of r50/VMD than the centrifugal atomizing nozzle (VMD = 153 μm). Our results indicated that the mortality limit can be reached at a concentration of an insecticide. The biocidal radius of a droplet is different from its actual size. The LD50 and translocation ability of insecticides contributed to their biocidal radius. Ratio of r50/VMD is an indicator of droplets' insecticidal potential. Smaller droplets generated by the air atomizing nozzle have higher insecticidal potential.