In this research, tartaric acid was used to enhance the hydroxyapatite coating on AZ31 Mg alloy substrate through post-treatment and direct addition methods, and the corrosion resistance and biological activity of the samples were investigated. The parameters of concentration, immersion time, and pH of the coating solution were optimized by Electrochemical Impedance Spectroscopy (EIS) and Direct Current (DC) Polarization techniques. According to EIS results in the post-treatment method, tartaric acid with a concentration of 1 g/L, pH = 9 and immersion time of 2 min, increased the corrosion resistance of hydroxyapatite coating from 3630 to about 18,763 Ω.cm