Abstract: The low melting point zone of CaO-Al₂O₃-SiO₂-MgO inclusions was analyzed and calculated by thermodynamic software FactSage. It is found that the low melting point zone can be divided into two different areas by alkalinity,and the sulfur capacity of the two areas was calculated and compared by using the KTH model. Then combined with the requirements of critical hydrogen 12Cr2Mo1 R on compositions and desulfurization,its applicable low-melting region was discussed. The results show that if inclusions are controlled at the high alkalinity zone,the contents(mass fraction) of CaO,Al₂O₃,and MgO are about 30%,15%,and 10%,respectively,the content of SiO₂ should be more than 40%,and it has a lager low melting point zone with higher SiO₂ content. If inclusions are controlled at the low alkalinity zone,the contents of CaO,Al₂O₃,and MgO are about 50%,45%,and 5%,respectively,the content of SiO₂ should be less than 5%. The sulfur capacity of the high alkalinity area is significantly less than that of the low alkalinity area. In both low melting point areas,the sulfur capacity is increased with the increase of alkalinity. The bigger the calcium/aluminum ratio is,the greater the sulfur capacity is increased with the increase of alkalinity. For the critical hydrogen 12Cr2Mo1 R,CaO-Al₂O₃-SiO₂-MgO inclusions should be controlled in the low melting point zone with high alkalinity,and higher alkalinity and calcium/aluminum ratio are better.