Nano-crystalline titania coatings were prepared by microarc oxidation (MAO) on titanium alloy (TC4) substrates in Na2CO3-KF electrolytic solution. The coating thickness was measured by an optical microscopy with a CCD camera. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the microstructure and phase composition of coatings. The results show that the coatings are porous nano-crystalline structures mainly composed of anatase and rutile (TiO2). With the increase of anode voltage, both the relative contents of rutile and the sizes of micropores increase gradually, whereas the sizes of the nano-crystalline decrease first and then increase. The prepared samples were employed to study the photo degradation characteristics of Rhodamine B. The results show that the photodegradation performance of the samples prepared under 220V is the best.