A water based coating composition containing 2-40 wt% resin, 0.015-30 wt% mixed solution including a filler modified by Si coinpound/surfactant/polymer and 0.05-10 wt% additives can be used for the production of an optical-usc polyester film. The described resin contains about: a. 20-50 wt, based on the weight of the coated layer, of composition A which is polyester resin; b. 10-40 wt%, based on the weight of the coated layer, of composition B which is alkylated melamine formaldehyde crosslinking resin; c. 20-80 wt%, based on the weight of the coated layer, of composition C which is acrylic resin. The coated polyester film has some superior properties such as high transparency, low haze value, good adhesion and anti-blocking property. It is suitable for optical applications such as a base film of the brightness enhance film or a base film for the light diffusing plate in a LCD.