The work aims to study the formation temperature of micro arc oxidation film on TC4 titanium alloy by preparation of micro arc oxidation composite film. The micro arc oxidation composite film on TC4 titanium alloy was prepared by adding the second phase particles (α-Al2O3, ZrO2, W) in the micro arc oxidation electrolyte. The maximum temperature of the film formation was detected by the fusion of the second phase particles. The second phase particles were found in the micro arc oxidation composite film. The particles of α-Al2O3, ZrO2 and W powder were all dissolved. The small second phase particles were dissolved in the film completely. However, the large size particles are not completely dissolved due to dynamics and short operation time of molten bath. The size of large particles became smaller and the outline became more rounded because of dissolution of surface and edge. In the composite film prepared by W powder with medium particle size of 50 nm, W particles were not found, but W element was found. The particles of W powder could be dissolved completely in the film due to small size. In the composite film made of W powder with medium particle size of 1 μm, particles of W powder were found and the particles were more rounded and smaller than 1 μm. This was caused by dissolution of partial particles (only dissolution of surface and profile). In the composite film, Al, Zr and W elements could be detected in the region without the second phase particles. According to the results of SEM and EDS, the maximum temperature of molten bath exceeds the melting point of W 3410 ℃ in the process of micro arc oxidation film formation.