The work aims to improve the bioactivity of the selective laser melting (SLM) produced Ti6Al4V alloy. The effect of different voltages on the preparation of calcium-phosphate bio-ceramic coatings on the SLM Ti6Al4V surface by micro-arc oxidation (MAO) technology was studied. The microstructure, morphology, and chemical compositions of MAO coatings prepared under different voltages were analyzed and studied by scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS) and X-ray diffraction (XRD). The biological activity of coatings was inspected by contact angle measurement, simulated fluid immersion experiment and subsequent FT-IR. A coating with a certain proportion of calcium and phosphorus was formed on the surface of SLM Ti6Al4V and well combined with the matrix after MAO treatment. The main phase of coating was anatase. Thickness of the coatings, the content of calcium and phosphorus and the content of anatase increased as the voltage increased. The coating produced by 300 V voltage had uniform surface and appropriate contents of Ca and P, which were 7.04% and 9.65%, respectively. The cross-section was uniform and the thickness was suitable, which was 3.19 μm. With the thickening of the coating, the content of matrix element Ti decreased and the content of Ca, P and O increased. The calcium phosphate ratio of the coating produced by 300 V was increased from 0.73 to 1.2 after soaked in SBF solution for 35 days, so the wettability of coating was better than that of SLM Ti6Al4V substrate and hydroxyapatite was generated. The optimum voltage to prepare the biological active coating on SLM Ti6Al4V by MAO is 300 V and the biological activity of Ti alloy is improved by MAO.