Bonding layers between tungsten carbide substrate and Al2O3 coating were investigated computationally and experimentally by CVD deposition under industrial production conditions, but longer time. In contrast to the common belief in the literature that the bonding layer is a cubic Ti(C,N,O) phase, titanium oxides were found. Energy dispersive spectroscopy and X-ray diffraction measurements were used to determine the compositions and structures of the bonding layer and the Al2O3 layer. It was found that the a-Al2O3 phase formed on the oxide bonding layer, and the k-Al2O3 phase formed without the bonding layer. A friendly user-interface for phase stability calculations has been developed by using Visual Basic for investigating industrial CVD process, particularly on the effects of processing parameters on the bonding layer structure. Phase stability calculations were conducted to explore the effects of processing parameters on the formation of various oxides. It was concluded that the decomposition efficiency of the gas precursors plays a critical role in the formation of oxides.