Silica aerogel thin films were prepared at ambient pressure by sol gel technique. Fourier transform infrared spectroscope(FTIR), scan electron microscope(SEM) and ellipsometer were used to characterize the structure and properties of the films. The refractive index of the resultant aerogel films is as low as 1.067, which corresponds to the porosity of 87.7 %, the density of 0.269×10 3 kg·m -3 , the thermal conductivity of 0.020W·m -1 ·K -1 (at 300K), and the dielectric constant of 1.52, These excellent properties mainly attribute to two step acid/base catalysis and the solvent exchange as well as the silylation on the surfaces of colloidal particles.