Adopting a gradient temperature method, hexagonal-cubic mixed boron nitride films were synthesized by MW-ECR radio frequency (RF) magnetron sputtering. The binding structure, the chemical composition, and the mechanical property of the films were investigated. The results show that there is a temperature threshold of the appearance of cubic BN film, and the hardness of the film increases with the increase of deposition temperature. Compared to the conventional methods the gradient temperature method is more efficient.