Abstract: Cr12MoV cold-work die steel is a high-carbon, high-chromium ledeburitic steel known for its high wear resistance, hardenability, quenching hardness, dimensional stability, as well as good thermal stability and comprehensive mechanical properties. It is widely used across multiple critical industries in China. As the demand for domestically produced high-quality die steels in advanced manufacturing sectors continues to grow, the need for high-quality Cr12MoV die steel is also gradually increasing. However, controlling the behavior of inclusions in this steel remains a significant challenge. To address this, this experiment utilized a laboratory MoSi₂ resistance furnace to conduct trace calcium treatment and cerium treatment on Cr12MoV die steel. Three test groups were designed, a blank group without calcium or cerium addition, a control group with only cerium addition, and an experimental group with both calcium and cerium addition. The effects of calcium and cerium addition on deoxidation and the evolution and mechanism of inclusion behavior in Cr12MoV die steel were analyzed using methods such as FactSage computational software, nitrogenoxygen analyzers, and scanning electron microscopy. The results show that as the amounts of calcium and cerium increase, the cleanliness of the steel gradually improves, and inclusions are progressively refined. The synergistic addition of calcium and cerium reduces the total oxygen (TO) mass fraction in the steel from 0.002 8% to 0.001 8%. In the steel without calcium or cerium addition, inclusions are primarily Al₂O₃ and magnesiumaluminum spinel. After adding 0.03% cerium, the inclusions transforms to mainly Ce-O-S type inclusions. With the addition of 0.001% calcium, the inclusions are modified to Ca-Al-O-S type inclusions. Subsequent cerium addition further transforms the inclusions into mainly Ca-Ce-O-S type inclusions, along with a small amount of aluminumcontaining inclusions. Thermodynamic calculation results indicates that a certain amount of cerium can reduce the size and area proportion of inclusions. When the mass fraction of calcium and cerium is 0.001% and 0.020%, respectively, the modification effect of inclusions in steel is the best. The above findings can provide a reference for controlling inclusion behavior during the production process of Cr12MoV die steel.