Through single-factor experiment, effects of current density, pH value, temperatrue,stirring speed on Cr-Al2O3 coatings were studied to obtian a suitable scopes. Orthogonal experiment L9(34) was designed to ascertain the influence of main complexing agent, auxiliary complexing agent, dispersant and AlCl3·6H2O on the thickness, appearance and the content of Al.Surface morphology, composition and microhardness of coatings were characterizated through using SEM, EDS and hardness tester respectively. Results revealed that under the optimized process condition and the optimized bath recipes namely: main complexing agent 18.9g/L, auxiliary complexing agent 3.85g/L, dispersant 2% and AlCl3·6H2O 12g/L, the Cr-Al2O3 composite coatings possess the thickness of 13.93 μm, the proportion of Al 10.90% and high microhardness of 867.9 HV.