The cleanness and usability of silicon steel are seriously affected by the type, number, size of the non-metallic inclusions. The evolution behaviors of the type, number, and size of inclusions in the non-oriented silicon steel slabs, which were subjected to different deoxidation processes (Si or Al deoxidation), were systematically investigated by using industrial testing and sampling analysis. The results indicate that the number and size of the inclusions are over larger during the starting-cast stage, and the reasonable cutting length for the first casting slab is 6 m. During steady-casting stage, the main types of the inclusions in Al deoxidization slab are Al2O3, Al2O3-MnS, Al2O3-MgO, Al2O3-AlN and their complex inclusions, and the main types of the inclusions in Si deoxidization slab are Al2O3, SiO2, Al2O3-SiO2 and a small amount of Al2O3-MnS, Al2O3-MgO complex inclusions. The number density and the occupation area fraction of inclusions in Al deoxidization slab are less than that in Si deoxidization slab. However, the stability of slab cleanliness in Al deoxidization process condition is inferior to that in Si deoxidization process condition.