BaTiO3 films were prepared by microarc oxidation (MAO) with an in-house built alternating current (AC) power supply in Ba(OH)2 solution in this study. The surface morphology, combinability with the substrate and phase composition of the films were investigated by XRD, SEM and TEM. The BaTiO3 films were annealed at a temperature range of 900 to 1200℃ and phase compositions were tested thereafter. The results showed that the BaTiO3 films were mainly composed of the primitive hexagonal phase with relatively small amount of tetragonal and amorphous phases. Moreover, the amount of amorphous phase decreased with the time of annealing. The transformation of BaTiO3 from hexagonal structure to tetragonal stucture became obvious until the annealing temperature reached 1200℃. The film consisted mainly of BaTiO3 tetragonal structure with ferroelectric property. The influence of annealing on surface morphology and mechanism of phase transformation of the films were also discussed. BaTiO3 films were prepared by microarc oxidation (MAO) with an in-house built alternating current (AC) power supply in Ba (OH) 2 solution in this study. The surface morphology, combinability with the substrate and phase composition of the films were investigated by XRD, SEM and TEM. The results showed that the BaTiO3 films were mainly composed of the primitive hexagonal phase with relatively small amount of tetragonal and amorphous phases. Moreover, the amount of amorphous phase decreased with the time of annealing. The transformation of BaTiO3 from hexagonal structure to tetragonal stucture became obvious until the annealing temperature reached 1200 ℃. The film consisted mainly of BaTiO3 tetragonal structure with ferroelectric property. The influence of annealing on surface morphology and mechanism of phase transformation of the films were also discussed.