A white balance adjustment method includes capturing a raw image by an image capturing device where an arrangement format of the raw image is BGb/GrR, color scale values of each color channel are extracted, the color scale values of all pixels in B, Gb, Gr, and R channels are separately scanned, and predetermined number ranges are used to classify the color scale values, then obtaining a cumulative proportion of color scale values in each channel is obtained. The cumulative proportions of each channel are compared with default minimum and maximum values, to obtain a more-than-maximum as a reference white, and a less-than-minimum as a reference black. The color scale values are re-quantized, according to the reference white and black, and a color histogram stretching method is applied to complete the white balance adjustment.