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The outstanding properties of silica aerogels encouraged continued efforts for the development of these materials since Kistlers pioneering work[1].They are highly porous,extremely light(densities in the range 3-500 kg/m3)[2],nanostructured and high surface area,The characterization methods of its surface area(N2 adsorption-desorption isotherms[3] at 77K of the degassed samples) is difficult, so we sought for a new method(UV-visible spectrophotometer) to explore the silica aerogels, in this paper, silica aerogels were synthesized by two-step sol-gel polymerization of tetraethoxysilane(TEOS) in alcohol and using supercritical drying , the dependence of surface area of silica aerogels on the sol-gel processing parameters have been studied,the silica aerogels were made in circular shapes by varying molar ratios of water(H2O)/TEOS.we studied the transmittance of silica wet gel by UV-Vis in different molar ratios of water(H2O)/TEOS, The structure and physical properties of the aerogels were investigated by several experimental methods,such as specific surface area analyzer and pore size analyzer(BET), 29Si solid state NMR spectra,transmission electron microscopy(TEM).The results indicated that silica aerogels are coherent and nano-porous solid,Its transmittance was the highest and the high specific surface area were 973.4m2/g when the molar ratios of water(H2O)/TEOS is 3, we also draw a conclusion that the transmittance of silica wet gel and the specific surface area is proportional relations,The structure of silica aerogels can be characterized by UV-Vis.