Abstract: Since the light-splitting film is always tilted, the separation between s- and p-component is inevitable. The separation has become a difficult problem to be solved in many applications. The material and structure of original film system were selected according to Costich and Thelen theories. A wide-angle depolarization flat-plate light-splitting film for three wavelengths (532nm, 633nm and 1315nm) was designed with all-dielectric materials by Needle synthesis method and Conjugate graduate refine method. The variation range of the incident angle in the air is 45°±5°. The design and analysis results show that the polarization separation of the film system in the spectral range of (532±10)nm, (633±10)nm and (1315±10)nm can meet the requirement of the depolarization in the wide-angle range.