We conducted experimental tests of the classification performance and flow field measurement in a turbo air classifier. In order to investigate the effects of operating parameters on flow field characteristics, we performed 2D velocity measurements of flow field in the classifier by laser Doppler velocimeter (LDV). The results indicate that different operating parameters have different tangential and radial velocity distributions in the passageway of rotor blades. The effect of different operating parameters on the radial velocity distribution is more intense than that of tangential velocity distribution. From 2D vectorgraphs of tangential and radial velocity, it is seen that the intensity, position, and rotation direction of a vortex is different under different operating parameters too. Air inlet velocity is held constant at about 8 m/s, and the intensity of the vortex is the least at a rotation speed of 600 r/min; air inlet velocity is held constant at about 18 m/s, and the intensity of the vortex is the least at a rotation speed of 1200 r/min. Under different operating parameters, we conducted the experiment of raw materials by employing ground calcium carbonate as the raw material. The rotation speed of the rotor is held constant at a value, and the high classification sharpness index k can be achieved around a critical air inlet velocity. The classification results testify the measurement results of flow field. (C) 2007 Elsevier Ltd. All rights reserved.