Plasma-sprayed HA coatings (HACs) on Ti-6Al-4V substrates with post-heat treatments were employed to improve the microstructural homogeneity, bonding strength and reliability of the HACs. A defect-healing effect can be recognized to diminish coating defects with the hydrothermal treatment, and 150°C hydrothermally-treated HACs shows a significant improved bonding strength than 600°C vacuum heating HACs because of its dense structure from the defect-healing effect. Low-temperature hydrothermal treatment demonstrates a more superior crystallization effect than vacuum heat treatment. Based on the statistical calculation by the Weibull distribution function, hydrothermally-treated HACs show a wear-out failure with a higher Weibull modulus than vacuum heating HACs. Hydrothermally-treated HACs possessed better reliability can be attributed to the suppression of defect content (about 2.6-3.2 volume %) and its smaller strength data fluctuation.