During the sand-making process, the stone powder produced by means of a vertical shaft impact (VSI) crusher affects the sand quality and pollutes the environment. This paper focuses on experiments and simulations with a stone powder separator (SPS) that is installed in a VSI crusher. Using FLUENT software, a coupling model of computational fluid dynamics (CFD) and the discrete phase model (DPM) is used to simulate the airflow distribution and particle traces in a VSI crusher. The stone powder separation and large particle retention performance are evaluated considering two important factors: the structure of the SPS and the air volume of the induced draft fan. The simulation results show that the air volume of the induced draft fan intuitively influences the particle traces and the distributions of particles of different sizes in the crushing chamber and the SPS chamber. There are many vortexes in the crushing chamber that cause the aggregate particles to be fully dispersed under the action of turbulence, and the SPS structure with radius decreasing from bottom to top can form an airflow velocity gradient in the SPS chamber and selectively remove particles according to size, thus improving the stone powder separation performance (SPSP). For this structure, when the air volume of the induced draft fan is set to approximately 40% of the maximum value, it can not only avoid large particles being massively removed but also ensure better SPSP of the device. Finally, the simulation results are verified by experiments. The results of this paper provide a reliable numerical model for the calculation of the flow field in a VSI crusher and provide a reference for the structural optimization of the stone powder separation device and for the selection of the best air volume of the induced draft fan.