The utility model relates to an optical polyester film which comprises a middle reflecting layer and diffusion layers arranged at the upper side and the lower side of the reflecting layer. The thickness of each diffusion layer is 1-30 micrometers. Reflecting layer particles are distributed on the reflecting layer. Diffusable particles are distributed on the diffusion layer. The particle diameters of the diffusable particles are 0.2-0.4 micrometer. The optical polyester film settles the problems of severe optical loss and low light saturation. Furthermore the optical polyester film has advantages of higher reflectivity and better light diffusion property.