The work aims to study the effect rules and action mechanism of the duty ratio on cathodic plasma electrolytic deposition (CPED) process by adjusting the experimental process. Al2O3 ceramics coating was fabricated via CPED technique on prepared TiAl alloy in Al(NO3)3 electrolyte under different duty ratios. Microstructure and compositions of different ceramic coatings were analyzed by analysis and test techniques including scanning electron microscopy (SEM), energy-dispersive spec-troscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD), and the material property test equipment such as eddy current thickness meter, surface profiler, Vicker’s hardness tester, scratch tester, etc. The thickness, roughness, hardness and binding strength of coating were also characterized. During the deposition, the duty ratio mainly affected the deposition adsorption and dehydration sintering of amorphous Al(OH)3 and the formation of crystalloid Al2O3. As the duty ratio increased, the relative crystallinity of ceramic coatings increased, the surface defects and cracks decreased, the uniformity, density and hardness improved, the thickness and binding strength increased firstly and then decreased and the surface toughness decreased firstly and then increased. When the duty ratio is 30%, the surface defects are less and the coating is bond with the substrate well. The lattice fringe of coating is neat and composed of α-Al2O3, γ-Al2O3, small amount of rutile-TiO2 and amorphous phase Al(OH)3. α-Al2O3 is 89.0%, the thickness is 47 μm, the surface roughness is 1.0 μm, the binding strength is 72 N and the hardness is 1010 MPa(HV200).