In order to improve the comprehensive utilization rate of calcium carbide slag and solve the separation problem of impurities, this work focuses on the impurity composition and occurrence form of calcium carbide slag. Cyclone separation process was used to separate the impurities from calcium carbide slag efficiently through a physical short range. The composition and occurrence form of calcium carbide slag were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), and chemical analysis. Finally, the properties of activated calcium oxide products prepared from raw slag, fine slag, and coarse slag were compared. The results showed that the cyclone separation can effectively separate the coarse particles and ferrosilicon components in the calcium carbide slag. The content of particles larger than 106 μm in the coarse slag was 35.21wt%, and the amount were only 0.40wt% and 0.11wt% in the raw slag and fine slag, respectively. The iron enrichment phenomenon in the coarse slag was remarkable, and the content increased from 0.25wt% to 1.14wt%. The content of acid insoluble matter in the fine slag was significantly reduced. The occurrence formed of impurities in calcium carbide slag were not changed during cyclone separation process. Element of carbon mainly existed in the form of simple substance and carbonate, aluminum and silicon mostly existed in the form of aluminosilicate, and sulfur mainly existed in the form of sulfate, sulfide, and mercaptan. The compressive strength of calcium oxide products prepared with fine slag as raw material can reach 5.1 MPa, which was about 50% higher than that of raw slag and coarse slag.