Microarc oxidation was performed on Ti-6Al-4V in an electrolyte containing calcium and phosphate ions.Samples were hydrothermally treated in different solutions containing calcium and phosphate ions.Various hydroxyapatite coatings were formed.It was found that hydroxyapatite coating is improved by the addition of calcium and phosphate ions in hydrothermal solutions.The addition of phosphate ions promotes the nucleation and growth of hydroxyapatite.But the effect of single calcium ions is not obvious.The addition of calcium and phosphate ions increases the nucleation and growth of hydroxyapatite,but decreases the preferred growth trend in some extent. Microarc oxidation was performed on Ti-6Al-4V in an electrolyte containing calcium and phosphate ions. Samples were hydrothermally treated in different solutions containing calcium and phosphate ions .Various hydroxyapatite coatings were formed. It was found that hydroxyapatite coating is improved by the addition of calcium and phosphate ions in hydrothermal solutions. The addition of phosphate ions promotes the nucleation and growth of hydroxyapatite. but the effect of single calcium ions is not obvious. The addition of calcium and phosphate ions increases the nucleation and growth of hydroxyapatite, but decreases the preferred growth trend in some extent.