Abstract: Direct casting of smelting slag into glass–ceramic is considered as an efficient way to simultaneously utilize “slag” and “heat” to prepare high value-added materials, owing to which has become a research hot spot. In this paper, silico–manganese slag was used as the main raw material, and silica, iron scale, and ferrochromium slag respectively as high-silicon, high-iron and chromium-containing modifiers. Furthermore, glass–ceramics were prepared using the Petrurgic one-step method. The Petrurgic one-step method is a heat treatment method for preparing glass–ceramic using controlled crystallization during slag cooling process. Using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM-EDS) and other tests, the effect of adding different modifiers on the mineral phase and properties of silicon–manganese slag glass–ceramics were discussed. Furthermore, the feasibility of preparing glass–ceramics by online modification of silicon–manganese slag was discussed based on thermal balance calculation and analysis. The research revealed that by cooling the modified slag to the crystallization temperature and annealing at 700 ℃, glass–ceramics that meet the performance requirements of natural granite can be obtained. Herein, the optimal sample of glass–ceramic had a flexural resistance of 74.67 MPa, bulk density of 2.95 g·cm⁻³, and water absorption rate of 0.08%. The crystallization performance of the modified slag was considerably improved compared with that of the original silico–manganese slag, and the iron scale and ferrochromium slag were more conducive to promoting the formation of granular or short rod-shaped pyroxene crystals with a particle size of 0.2–0.5 μm. The obtained products have pyroxene group crystals, such as augite (Ca(Mg,Fe,Al)(Si,Al)₂O₆) and johannsenite (CaMnSi₂O₆) with a solid solution of Fe and Mn ions. The addition of modifiers altered the occurrence form of Mn ions in the silico–manganese slag. Mn ions in the original slag were mostly found in the form of glass phase and manganese sulfide, whereas Mn ions in the modified samples were mostly found in johannsenite. Microcracks appeared especially in the samples modified with silica after heat treatment, and the crystal density of pyroxene was greater than that of the glass matrix, and volume shrinkage caused by its precipitation was one of the causes of crack formation. During the modification process, it was observed that when 10% silica and iron scale were added as modifiers, the sensible heat of slag was greater than the melting endothermic heat of the modifier, and no additional heat was required in the modification process. Furthermore, when ferrochromium slag was used as a modifier, the glass–ceramic was prepared by the hot-state mixing method between silico–manganese slag and ferrochromium slag.