Abstract: Droplet size distribution, as an important indicator, is usually used to evaluate the performance of nozzles. Laser particle analyzers are usually adopted for the droplet size distribution measurement but the apparatus have the disadvantages of high expense, complicated operation and can not obtain results conveniently. In this paper, a Newton iterative method based on ULLN model was designed to determine unknown parameters in this model by using information provided by droplet sizes including Dv0.1, Dv0.5, Dv0.9, and then the expressions of the model were definited. The volume percent of a specific range of droplet size was figured out by using numerical integration with Simpson method. This method could determine volume percent of any ranges of droplet size in theory, because ULLN model has been determined after those calculation progresses above. In the last, comparison between results calculated by this method and that by DRIFTSIM program revealed that the method in this research had higher calculation accuracy than DRIFTSIM program.