We deposited hBN films on silicon substrates by RF magnetron sputtering, and investigated the stability of the hBN films to the moisture. The hBN films including a large quantity of oxygen impurities were apt to be attacked by water vapor, and the hydrolytic process of the hBN films was studied by FTIR spectra. According to the analysis of FTIR, the main reason for the hydrolysis is the existence of boron oxides in hBN films, and the result of the hydrolysis is the formation of boric acid crystals. We sintered the hBN targets at high temperature in order to prevent oxygen from entering into the hBN films. Both FTIR and XPS results show that the hBN films have a good waterproof performance after our technology improvements because of the limit to oxygen impurity. Finally, pure and stable hBN films were obtained successfully.