In response to the national "energy saving and carbon reduction" strategy and the requirement to reduce the production cost of cement clinker, experimental research and practical application optimization were conducted on two 2 500t/d cement clinker production lines for partially substituting limestone with magnesium slag in raw meal proportioning and clinker burning. By analyzing the basic characteristics of magnesium slag and the changes in the quality of raw materials, fuels, raw meal, and clinker before and after using magnesium slag, targeted measures such as equipment modifications and process parameter optimization were proposed. These measures effectively resolved production issues arising during the magnesium slag burning process, including scaling in the precalciner cone, formation of long and thick coating in the rotary kiln, and instability in clinker quality. Practice shows that after partially substituting limestone with magnesium slag, the precalciner kiln system achieved stable operation. The actual coal consumption decreased by 8.1kg/t.cl, the standard coal consumption decreased by 6.21kg/t.cl, and the carbon emission reduction in clinker reached 0.066 7t/t.cl. Meanwhile, the 3d and 28d compressive strengths of clinker increased by 5.2MPa and 2.2MPa, respectively, achieving multiple goals of saving coal, reducing carbon emissions, lowering costs, and improving quality, has provided a practical reference for the resource utilization of industrial waste residues and the green, low-carbon development of the cement industry.