This paper reports the formation and control of the four major macro-inclusions in alloy steel during steel ingot production. We selected AISI stainless steel, AISI H13 tool steel, DIN 1.4104 stainless steel samples for our laboratory tests. From micro-structure observation and composition analysis, we concluded that the primary sources of the macro-inclusions are runner refractories, mould powder, reoxidation, and inclusion agglomeration. Methods for eliminating and avoiding the macro-inclusions are also presented.