Cut size is regarded as an important indicator for evaluating the classification performance of turbo air classifiers. However, traditional methods of cut size calculation by theoretical analysis have some deviations. In this paper, a new strategy was introduced to determine the cut size using the FLUENT discrete phase model (DPM) coupled with material experiments. The simulation results revealed that: the closer the feeding point position approached the inner edge of annular region, the shorter the time the particle moved into the area between the two neighboring blades of the rotor. The same small diameter particles which were fed at three different positions in annular region could all enter into the area between the two neighboring blades of the rotor, and ultimately were discharged by the fine powder outlet. When air inlet velocity was 8 m/s, rotor cage rotary speed was 800 r/min, the cut size of talcum powder could be calculated as 30-40 mu m, and the cut size of quartz sand powder could be calculated as 40-50 mu m. When rotor cage rotary speed was 1200 r/min, the cut size of talcum powder could be calculated as 20-30 mu m, and the cut size of quartz sand powder could be calculated as 30-40 mu m. The contrastive experiments of material classification were in good agreement with simulation results. Simulation method provides a new method to determine the cut size of a turbo air classifier, as well as provides a reference method to study the cut size of various types of classifier. (c) 2012 Elsevier B.V. All rights reserved.