Abstract: Al₂O₃ ceramics is in-situ synthesized on the.surface of martensitic stainless steel, ignited by strong current. The synthesizing material are analytically pure Fe₂O₃, powder and Al powder which graininess is less than 10 μm. The microscopic structure of the synthesized Al₂O₃, ceramics and the transition region between Al₂O₃, and martensitic stainless steel is investigated with optical microscope and scanning electron microscope. The constituent of corresponded parts is taken with electron probe microanalyzer. The results show that the microscopic structure of synthesized Al₂O₃, ceramics layer is mainly composed by ceramic phase Al₂O₃ and a little of α-ferrite and spinel phase Al₂O₃·FeO in Al/Fe₂O₃, self-propagating high-temperature synthesis system. Excessive Al powder in the material is advantageous to synthesize ceramic phase; the thickness of synthesizing material body is not less than 2.0 mm in order to get well-synthesized Al₂O₃ martensitic stainless steel composite material.