A novel vortex finder (slotted vortex finder) was designed to improve cyclone separator performance. The gas flow in axial-inlet cyclone separator with the novel vortex finder is simulated by means of Reynolds Stress Model (RSM). The computational results of the flow patterns in cyclone separator are compared with the experimental ones, and the results show that RSM offers a robust, reliable modeling option for such flows. Three dimensional gas flow simulation results indicate that the gas flow exits the separator through two pathways. One part of the gas spirals down from outer annular space to outer separation space and dust hopper, then spirals upward in the inner part of separator, and finally exits the separator. The other gas flow enters the vent pipe through the slots in vortex finder rather than entering the separation space. The simulation results show that the latter part flow accounts for 54% of the total gas flow. Diversion of gas pathways has three advantages. Firstly, the 54% of the gas-solid flows can be separated by slots due to the novel vortex finder. Secondly, the results also indicate that there are almost no short circuit flows under the inlet of the slotted vortex finder. Thirdly, the slotted vortex finder reduces the flow swirling intensity and undesired instabilities, and thus the slotted vortex finder can reduce pressure drop. (C) 2016 Elsevier B.V. All rights reserved.