The structure of the vortex finder has an important influence on the pressure drop and separation efficiency of a cyclone, which mainly governs the separation process. In this paper, the traditional vortex finder is slotted on side wall and its bottom is closed, i.e., a slotted vortex finder. The impact of slotted vortex finder on the separation performance of a cyclone is explored by using numerical simulation and experimental validation. Specifically, the gas phase is studied by the Reynolds stress model (RSM), and the particle phase is simulated by the discrete phase model (DPM). The simulation results are in good agreement with the experimental results, revealing higher prediction accuracy. The results indicate that the slotted vortex finder can effectively suppress the generation of the downward swirling flow at the center of the vortex finder and decrease the turbulence intensity at the bottom of the vortex finder and the outer vortex, thereby decreasing the energy loss and increasing the separation efficiency. When the slot length is 0.2De, the slotted vortex finder can reduce the pressure drop by 143.33 Pa while increasing the collection efficiency by 5.51%.