A barcode decoding method includes steps of capturing an image of a barcode; dividing the image into a plurality of blocks and dividing the blocks into a plurality of longitudinal regions; calculating a representative gray level for each of the blocks; dividing at least one of the longitudinal regions into a relative majority region and a relative minority region; defining one of the relative majority region and the relative minority region as a normal region and defining the other of the relative majority region and the relative minority region as an abnormal region; selecting a block from each of the normal regions to set a scanning line; and performing a binarization algorithm for a gray level distribution of the scanning line to decode the barcode.