In this research, tantalum was modified by two-step hydrothermal treatment, and magnesium-doped tantalum oxide nanorods with narrow rod spacing were obtained on the surface of tantalum. The morphology and microstructure of nanorods were observed with the change of the doping amount of magnesium. In the process of hydrothermal treatment, the best concentration of magnesium acetate solution was 0.05 M, and the content of Mg in tantalum oxide nanorods reached 4.25 at%, and magnesium was doped in the form of Mg2+. The roughness was measured by AFM and the roughness of Ta2O5 nanorods and Mg-Ta2O5 nanorods was higher than that of pure tantalum. ICP results showed that the precipitation rate of magnesium ions in normal saline increased greatly at first and then slowed down. Ta2O5 nanorod could not induce apatite until 12 days while apatite deposited on the surface of Mg-Ta2O5 nanorod coating for less than 8 days in biological activity test. Mg-Ta2O5 nanorod coating effectively improved the biological activity of tantalum substrate.