The work aims to study the effects of various positive and negative duty cycles on the growth mechanism, structure and corrosion resistance of red mud (RM) plasma electrolytic oxidation (PEO) composite ceramic coatings on 5005 aluminum alloy surface. The ceramic coatings were prepared on the surface of 5005 aluminum alloy at various positive and negative duty cycles with RM as electrolyte additive by PEO technology. Phase composition, microstructure, constitution and corrosion resistance of ceramic coating were tested and characterized with X-ray diffractometer (XRD), scanning electron microscope (SEM) with energy disperse spectrometer (EDS) and electrochemical workstation. When the positive or negative duty cycle was increased separately, the current increased and the breakdown discharge function improved. With the increase of diffusion rate of RM particles and the concentration in the coating formation, the ceramic coating grew faster with higher thickness and darker color, but was significantly affected by the negative duty cycle. When the reaction time was 20 min, the maximum thickness could be 27.70 μm and 35.82 μm, respectively. The coating consisted mainly of γ-Al2O3 and a small percentage of amorphous phase, α-Al2O3 and RM minerals including Fe2O3, CaCO3 and SiO2. α-Al2O3 and Fe2O3 went up rapidly with the increase of negative duty cycle, which could be up to 6.40% and 2.86%, respectively. With the increase of duty cycle, the coating compactness and corrosion resistance firstly increased and then decreased, but the effect of negative duty cycle was greater than that of positive duty cycle. When the positive duty cycle was 24%~42% and negative duty cycle was 12%~18%, the coating was compact with smaller corrosion current density and corrosion rate, and larger impedance, showing a good corrosion resistance. The structures and properties of PEO coatings are affected by positive duty cycle less than by negative duty cycle, and a RM-PEO composite coating with dense structure and good corrosion resistance can be fabricated by proper proportion of positive and negative duty cycles.