Binarization method and system for two dimensional code images is provided. Each block region has a different grayscale threshold. Thus, for each block region, whether a pixel in the block region is determined as black or white restoring process is not solely based on the grayscale value of the pixel itself, but also an average grayscale value of a predetermined area specified for a block region where the pixel locates. That is to say, when the predetermined area in which the block region locates has generally a larger grayscale value, the grayscale threshold corresponding to the block region may become larger, and vice versa. Because the grayscale threshold of a block region is closely related to grayscale values in a background of this block region, external circumstance interference may be prevented from an obtained binary result, producing a clear binary image accordingly.