The monodisperse collodial SiO2 sol was prepared by sol-gel process using tetraethylorthosilicate (TEOS) as precursor and ammonia as catalyst. Hexadecyltrimethoxysilane (HTMS), as a modifier, was added into the sol to passivate the surface of the silica particle . Silica antireflective (AR) coatings were then prepared from different SiO2 sols by dip-coating method. UV-Vis-NIR spectrometer, Fourier transform infrared spectroscopy, transmission electron microscope, Scanning Electron Microscopeand water contact angle measurement were employed to analyze the optical property, microstructure, surface morphology and environmental stability of the coatings. The results show that the HTMS modified silica AR coating can achieve a high transmittance of ~99.8% and possess excellent environment stability.After been placed in an ambient with relative humidity higher than 90% for 2 months, the peak transmittance of the silica AR coatings modified with HTMS decreased only by 0.3%.