Phase composition and microstructure of hydroxyapatite (HA) significantly affects the biological and mechanical properties of final hydroxyapatite (HA) coating. In the present study, HA coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS) using different spray parameters. The influence of spray parameters on the composition and microstructure of the coatings were investigated. To understand the formation mechanism of HA coatings, the in-flight particles and splats were examined as well. The morphologies of coatings surface, cross-sections, initial powder, in-flight particles and splats were characterized by scanning electron microscopy (SEM). Xray diffraction (XRD) was employed to analyze the phase composition. Three typical HA coatings were fabricated. The results indicated that the coating composition and microstructure were tightly related to the melting state of inflight particles. And this was influenced by the spraying parameters. The formation mechanisms of these coatings were discussed.