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Si-Co-Y co-deposited coating was prepared on the surface of TiAl alloy by pack cementation process. The microstructure, formation mechanisms and oxidation performance at 950 ℃ of the coating were analyzed. The obtained Si-Co-Y co-deposition coating is compact and possesses multilayer structure: mainly composed of a TiSi₂ superficial zone, a TiSi₂ and Ti₅Si₄ mixed outer layer, a Ti₅Si₃ middle layer and a TiAl₂ inner layer. The growth of the Si-Co-Y co-deposited coating is controlled by inward diffusion of Si, and followed an orderly process of depositing Si first and then Co. High-temperature oxidation tests show that the Si-Co-Y co-deposited coating has good anti-oxidation resistance, due to the formation of a protective oxide scale that composed a mixture of SiO₂, TiO₂ and Al₂O₃. The growth of the oxide scale on the coating followed a parabolic law, and the parabolic rate constant of oxidation weight gains is about 6.3×10_-2 ^mg₂^/cm₄^h_1/2^, lower than that of the TiAl substrate by about one order of magnitude.