Data from a thermodynamic database and the calculation software FactSage were used to investigate the phase diagrams of the MnO-CaO-SiO₂-Al₂O₃ system in cutting-wire steel and the effects of oxide components on the low-melting-point (LMP) zone in the corresponding phase diagrams. Furthermore, the activities of oxide components in the quaternary system at an Al₂O₃ content of 25wt% were calculated. The contents of dissolved [Al] and [O] in liquid steel in equilibrium with LMP inclusions in the MnO-CaO-SiO₂-Al₂O₃ system were optimized. The results show that the MnO-CaO-SiO₂-Al₂O₃ system possesses the largest LMP zone (below 1400°C) at an Al₂O₃ content of 25wt% and that the CaO content should be simultaneously controlled in the range of 40wt% to 45wt%. The activities of the oxide components CaO, MnO, and SiO₂ should be restricted in the ranges of 0 to 0.05, 0.01 to 0.6, and 0.001 to 0.8, respectively. To obtain LMP inclusions, the [Al] and [O] contents in cutting-wire steel must be controlled within the ranges of 0.5×10^-6 to 1.0×10^-5 and 3.0×10^-6 to 5.0×10^-5, respectively.