A boundary judging method for a 3D display apparatus includes: dividing each of a first picture and a second picture to be displayed into a plurality of theoretical pixel units and determining color components of each of the theoretical pixel units; determining, for each sub-pixel for displaying each of the first and second pictures, a luminance of the each sub-pixel according to a color component, corresponding to a color of the each sub-pixel, of the theoretical pixel units that are covered by a preset sampling region corresponding to the each sub-pixel and that belong to the corresponding picture; and determining, for each of the first and second pictures, a boundary between adjacent two of sub-pixels of each color in the corresponding picture according to a luminance difference between the adjacent two of the sub-pixels of the each color.