1. A method for optimizing occlusion occurring in an augmented reality system comprising one or multiple depth cameras and one or multiple two-dimensional cameras, the method comprising the steps of: (a) capturing, by the one or multiple depth cameras, a scene and an object in the scene to obtain initial depth data, and capturing, by the one or multiple two-dimensional cameras, the scene and the object to obtain two-dimensional image data; (b) in-painting the initial depth data to obtain in-painted depth data; (c) performing a depth buffer calculation according to the in-painted depth data and a virtual model to obtain an occlusion relationship between the object and the virtual model, and generating an occluded partial image according to the two-dimensional image data and the virtual model; (d) estimating a partially approximated polygon according to the occluded partial image; and (e) generating an occluded result according to the partially approximated polygon, the two-dimensional image data and the virtual model, wherein the step (b) comprises: (b1) transforming the initial depth data into single channel grayscale image data; (b2) in-painting the single channel grayscale image data to fill depth values into data pixels without depth values in the single channel grayscale image data, and thus obtaining in-painted single channel grayscale image data; and (b3) converting the in-painted single channel grayscale image data into depth values to obtain the in-painted depth data.