Sb-doped SnO2/SiO2 nano-composite thin films prepared by sol-gel dip-coating method have been studied. By using X-ray diffraction (XRD), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy, detailed investigation on the structure and morphology of the films has shown the crystalline grain size of Sb-doped SnO2/SiO2 thin films is about 34nm, with larger specific surface area and duty porosity, which is fit for gas-sensing materials. The adulteration of SiO2 particles leads to the condensation of Sn-OH and the strengthening of gel network, and improve the adhesion of the films. In addition, the optical properties of the thin films were studied by UV-Vis spectra and p-polarized light reflectance angular spectrum. The results showthat the optical transmissivity of Sb-doped SnO2/SiO2 thin films is higher, near 95% in visible spectrum range, the measured optical gap is found equal to 3.67eV, also the films take on smaller refractive index and extinction coefficient compared with those of the SnO2 and Sb:SnO2 films, which is compatible with the semiconductor substrate in the solar cell. Further, the gas-sensing test was made to three kinds of gas C3H8, C2H5OH and NH3 in our novel high sensitive scheme for optical film sensors. The results indicate that Sb doping to SnO2 films greatly improves the gas sensitivity to C2H5OH, and the gas sensitivity of Sb:SnO2/SiO2 nano-composite thin films are higher than that of Sb:SnO2 thin films. The detection sensitivity of this optical film sensor is available to 10-1ppm provided that the resolution of reflectance ratio is 10-2.