By using the transfer-matrix method, the multilayer films of photonic crystal composed of SiO2 and TiO2 with high-transmissivity are designed. The characteristics of transmission spectra of the multilayer films are studied. Based on the theory of equivalent layer, the structure of photonic crystal is modified to improve the transmittance in the pass band around specific wavelength, and the optimal parameter is obtained. The results indicate that the minimum transmittance of the optimal structure with lattice paramenter of 150 nm, filling ratio of 0.346 and periodicity of 6, is also up to 96.5% at 400 nm. No matter the incident wave is TM model or TE model, the transmittance do not change significantly, when the incident angles changes from 0° to 45°. The structure can be used for air purification device to improve the photocatalytic efficiency of SiO2 and TiO2 films.