Abstract: To combat plant pests and diseases, spraying pesticide is an efficient and timely control method. The increasing use of a wide range of toxic chemical pesticides deliberately released into the environment can cause important problems such as human health threats, bioaccumulation and pest resistance, and soil and groundwater pollution. In response to concerns about the effects of chemical pesticides on environments and human health, there have been significant interests in biological pesticide technology with low toxicity, less residue, and reduced pest resistance. Biopesticide technology is limited in real applications, due to the lack of appropriate sprayer and standard technology. In this paper, a rotary cage atomizer for biopesticide was developed. The influence of biopesticide atomizer structure (cage diameter and cage mesh number), operational parameters (flow rate and rotational speed), and liquid types (bacillus thuringiensis and beauveria bassiana) on atomization performance and biopesticide application efficacy was investigated using PIV and a Winner laser diffraction particle analyzer. The pattern of liquid inlet was fixed experimentally by the droplet's flow field uniformity. The impacts of individual factors on droplet size were analyzed using a T-test to eliminate inter-correlation among the variables of interest. A multiple linear regression model, which predicted the volume median diameters (VMD), was established. The model showed a high degree of correlation with the experimental results. The model took into account not only the cage diameter, but its number of cage meshes, the liquid flow rate, and rotational speed of the cage. Furthermore, a histogram and normal P-P plot of standardized residuals were used to assess the model's goodness-of-fit and the measured data were also analyzed to prove model fitness and feasibility. Finally, the optimal combination of biopesticide rotary atomizer structure and operational parameters was implemented. The results indicated that the cage atomizer's liquid inlet of bilateral symmetry is better than the unilateral pattern to improve the distribution uniformity of droplets. The rotational speed of the rotary cage atomizer should not be too high to maintain the viability and infectivity of biopesticides. Results from this paper provide a case study showing how to spray biopesticide to treat plant pests and diseases effectively by using proper sciences and technologies.