Abstract: In order to investigate the distribution characteristics of particle size of tobacco casing atomized by a two-fluid nozzle and further optimize tobacco casing process, the factors including the type of ejecting medium, gas/liquid ratio, liquid circuit temperature and casing properties were studied with a two-fluid nozzle test device and a laser spray measurement system. Moreover, an empirical model of Sauter mean diameter (D₃₂) was established on the basis of dimensional analysis. The results showed that:1) When the flow rate of ejecting medium or that of liquid circuit was constant, D₃₂ decreased gradually and the uniformity index (N) increased slightly with the increase of gas/liquid ratio. 2) When the other conditions were the same, D₃₂ and N did not significantly change with the rise of water temperature. However, D₃₂ decreased gradually and N did not change significantly with the rise of casing temperature. 3) When the other conditions were the same, D₃₂ increased gradually with the increase of casing viscosity. Comparing with water, the N of different casings did not significantly change when compressed air was used as ejecting medium, however, it decreased significantly when steam was used as ejecting medium. 4) When water and casing were atomized with compressed air and steam separately, the average relative error between predicted value and measured value of D₃₂ ranged from 2.3% to 3.9% and the maximum relative error was 15.2%.