Droplet size distribution is a crucial parameter of atomization process besides droplet mean diameter. In this paper, the finite stochastic breakup model (FSBM) of prefilming air-blast atomization process has been proposed according to the self-similarity of droplet breakup. There are four parameters in FSBM, which are the initial droplet diameter D-0, the maximum stable droplet size D-c, the minimum mass ratio of a sub-droplet to the mother droplet a, and the droplet breakup probability P(D). The simulation results of droplet size distribution with this model agreed well with the experimental results of prefilining air-blast atomizers. With this model, the nonlinear relationship between the mean droplet diameters and droplet size distribution of the air-blast atomization process can be predicted exactly. (c) 2005 Elsevier Ltd. All rights reserved.