Objective To study the oxidation resistance and oxidation-resistance mechanism of atmospheric plasma-sprayed NiC- oCrAlY / Al2 O3 wear-resistant coatings at 850 ℃ . Methods The NiCoCrAlY / Al2 O3 composite powder was prepared by the technolo- gy of spray granulation, chemical and metallurgical coating and solid state alloying. The NiCoCrAlY / Al2 O3 composite coating was prepared by atmospheric plasma-spray technology using the prepared powder on the surface of 45# steel. The microstructure and phase composition of the powder and coating were studied by SEM and XED. The oxidation kinetic curve at constant 850 ℃ was explored with muffle furnace and the oxidation resistance mechanism of the APS sprayed NiCoCrAlY / Al2 O3 composite coatings was investigated through analysis of morphology of the coating surface after 96 h of oxidation. Results The Al2 O3 was evenly and closely coated with NiCoCrAlY alloy and the thickness of NiCoCrAlY alloy was 3 ~ 5 μm. The phase compositions of composite powder were mainly NiCoCrAlY and Al2 O3 without other impurities. The oxidation kinetics curves of the coatings can be divided into three stages: severely sloping, parabolic and slightly parabolic stages. The value of oxidation weight gain was about 4. 9 mg / cm2 after 96 h of oxidation. The oxide film was formed and the phase compositions of oxide film were Al,O, Cr and Ni according to the EDX a- nalysis. Conclusion The NiCoCrAlY / Al2 O3 composite coating exhibited excellent oxidation resistance property. The reason of oxi- dation resistance of the coating was the oxidation of Ni, Al and the addition of Al2 O3 .