The straight guide blade of a turbo air classifier was modified to obtain ultrafine powder with narrow particle size distribution, and to improve classification precision. The modification involved positively or negatively curving the straight blade. The structural effects of the straight, positively bowed, and negatively bowed blades on the inner flow field of a turbo air classifier were all simulated with the FLUENT software. The numerical simulations indicate great improvement in the annular region tangential and radial velocity distributions of the positively bowed guide blade, compared with the straight and negatively bowed blades. Air velocity fluctuations on the outer cylinder of the improved guide blade are decreased in the height direction. Also, the radial velocity is decreased and the tangential velocity is increased using the positively bowed blade. As a result, the classified particles are cut smaller than with the straight and negatively bowed blades. The inertia rotating vortex between blades is decreased, and the flow field becomes stable. Material classification performance experiments were also performed. The results thereof demonstrate that the positively bowed guide blade improves the classification precision and decreases the particle cut size. These actual experimental results confirm the computational fluid dynamics simulation results and the feasibility of the modified guide vane in engineering applications. (C) 2012 Published by Elsevier B.V.