The interfacial microstructure of cubic boron nitride (c-BN) film deposited on single silicon substrate using magnetically enhanced active reaction evaporation (ME-ARE) has been investigated through thinning methods, in which X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) absorption spectroscopy were used for compositional and microstructure analysis. c-BN film was etched at size 4 x 4mm(2) by argon ion in XPS equipment to obtain depth concentration profile of the BN film and B 1s XPS spectra at different etching depth. FTIR was alternately used to determine the microstructure of the BN film at different etching depth. The results show that a thin layer of hexagonal boron nitride (h-BN) phase exists at the interface between c-BN layer and substrate. In addition, transmission electron microscopy and selected area electron diffraction further confirm above the conclusion.