Abstract: Experimental study on removal of non-metallic inclusions in non-oriented silicon steel obtained from industrial production by CaSi wire feeding during RH refining process was carried out.The thermodynamics of CaS inclusion formation was analyzed,the morphology and the size distribution of inclusions were observed,and the numbers and types of inclusions were also determined for the steel specimens treated under different calcium treatment conditions.Furthermore,the variation of inclusion characteristics after calcium treatment was discussed.The results show that due to calcium treatment,the formation of MnS and AlN inclusions can be restrained,and the aggregation,flotation and removal of micro-inclusions can be efficiently boosted.As a result,the cleanliness of liquid steel is noticeably improved.The main types of inclusions are single phase of CaO,and some complex inclusions are composed of CaO,SiO₂ and MgO,and no CaS inclusion is found after an appropriate calcium treatment.The size of all the inclusions is in the range of 2 μm to 20 μm,and their amount is about 1.8×10⁵/mm³.