The improvement of the inlet geometry of the cyclone is conducted in this study based on the previous works, i.e., the cyclone inlet has a certain inlet section angle. The gas flow fields in cyclones for the different inlet section angles were calculated by means of computational fluid dynamics (CFD) technology, and the inner flow field geometry of these cyclones were compared. Additionally, the pressure drops and separation efficiencies of these cyclones were studied by experiments. The results indicate that the inlet section angle can make the flow filed in the cyclone be propitious for particle separation, and improve the separation performance effectively. At the same inlet velocity, with increasing the inlet section angle, both total separation efficiencies and grade efficiencies increase, and the pressure drops reduce greatly. Combining the change tendency of the pressure drop and the separation efficiency, a conclusion can be obtained, i.e., the optimal angle should be 45, for the range of the inlet section angle in this study. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.