Four kinds of typical plasma electrolytic oxidation (PEO) coatings were prepared on TC4 alloy to investigate the influence of electrolyte composition on the corrosion behavior and tribological performance of the PEO coatings. The results show that both the corrosion behavior and tribological performance of the PEO coatings are highly dependent on the electrolyte composition. The PEO coating fabricated from the electrolyte containing NaH₂PO₂ exhibits the best corrosion resistance owing to its denser inner layer. The PEO coating prepared from the electrolyte containing NaAlO₂ reveals the best tribological performance due to the generation of Al₂O₃. To prepare a PEO coating with satisfying corrosion resistance and wear resistance, a composite PEO coating was fabricated from the electrolyte containing NaH₂PO₂ and NaAlO₂.