Abstract: To study the source of inclusions in casting billets, 10% BaCO₃, 10% SrCO₃, and 10% La₂O₃ were used as tracers into the steel ladle, tundish covering flux, and tundish-coating refractories, respectively, during the production of non-oriented silicon steel. The steel and slag samples were taken from the related working procedure, and scanning electron microscopy (SEM) and a mi-croscope were used to analyze the morphology and composition of inclusions. Experimental results show that the large inclusions in non-oriented silicon steel are mainly SiO₂, Al₂O₃, and aluminosilicate, resulting from the protecting slag and secondary oxidation.