The work aims to study the influence of negative current density on bioactivity coating formed by micro-arc oxidation (MAO) on TC4 alloy in the electrolyte with Ca(H2PO2)2 and Ca(CH3COO)2?H2O, which provides a reference for the biological modification of titanium alloy. The bio-ceramic coating was prepared on TC4 alloy by AC pulsed MAO technology. The growth process, structure and chemical composition of MAO coating formed under different negative current densities were analyzed by SEM, EDS, XRD and EIS. The scratch test was used to characterize the effect of negative current densities on the bond strength of the film/substrate. When titanium alloy was micro-arc oxidized in the electrolyte with Ca- and P-, the MAO ceramic coating was composed of rutile-TiO2, anatase-TiO2 and a small amount of Ca- or P- amorphous compounds. However, the content of Ca and P slightly increased and the relative proportion of anatase-TiO2 gradually decreased with the increase of negative current density. Meanwhile, the molar ratio of Ca/P always stayed around 1.67. Although the application of negative current would decrease the growth rate of MAO coating, the micro-cracks on the coating surface decreased obviously and the adhesive strength of coating/substrate increased greatly. The critical load (Lc) for the cracking of the coating increased from (15.1±0.5) N when 0 A/dm2 to (19.9±0.5) N when ?3 A/dm2 was used in MAO process. The application of negative current can increase the coating/substrate adhesive strength and decrease the micro-crack defects in the coating, which is more helpful to the bonding of titanium alloy implant and bone in theory.