Silica aerogel with ultra high porosity(>90%) and large surface area(~1000 m2/g) is prepared by supercritical drying of wet gel. We observed the change of surface bonding states of aerogel which contains hydroxyl groups (OH). physisorbed water and some alkoxyl groups (OR, R : C2H5 or CH3) before and after the surface treatment using X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy. Almost all of hydroxyl groups and alkoxyl groups were removed by thermal treatment at 80$0^{circ}C$ under vacuum but single isolated OH bond (Si-OH) remained. In order to achieve the OH free surface of aerogel thermally treated aerogel was successively retreated with halogen compounds (NH4F and Na2SiF6) and we could achieve the OH free aerogel with Na2SiF6