The modified tailings containing Fe₂O₃ after reduction of copper slag were used as the raw materials for the preparation of gehlenite-based glass-ceramics. The effect of Fe₂O₃ content on the crystallization behavior, microstructure and mechanical properties of glass-ceramics were investigated by Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning electron microscopy with an energy dispersive spectrometer (SEM-EDS). The results show that when the Fe₂O₃ content increases from 0 wt% to 4 wt%, the crystallization peak temperature of base glass decreases and the crystallization activation energy of base glass decreases firstly and then increases. The minimum crystallization activation energy is 237.71 kJ/mol when the Fe₂O₃ content in base glass is 1 wt%, resulting from the highest content of glass modifier [FeO₆]-octahedral in the glass. The crystallization index indicates that the crystallization method of base glass is surface crystallization, irrespective of the Fe₂O₃ contents of the base glass. Although the crystallization rate is slow resulting from the limited crystallization sites provided by Fe₂O₃, the glass-ceramics with 2 wt% Fe₂O₃ has a good comprehensive performance. When the nucleation process is at 850℃ for 120 min and the crystallization process is at 980℃ for 120 min, the flexural strength, microhardness, volume density and water absorption of the glass-ceramics with 2 wt% Fe₂O₃ are 138.26 MPa, 872.19 HV, 2.81 g/cm³ and 0.16%, respectively.