We report a new method to prepare boron nitride (BN) thin films on Si (100) substrates in an Ar-N2-BC13-H2 gas system by magnetron arc enhanced plasma chemical vapour deposition. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize the films. The FTIR spectra show that the deposited boron nitride films experienced a transition from pure h-BN phase to a cubic-containing phase with the variation of arc current ranging from 10A to 18A. The BN film with 42% c-BN was obtained without substrate bias voltage. In the gas system of Ar-N2-BCl3-H2, h-BN can be preferentially etched by chlorine. The chemical etching effect of chlorine allows the formation of c-BN without substrate bias voltage, which may develop a new perspective for the deposition of high quality c-BN film with low stress.