A white balance adjustment method includes capturing a raw image by an image capturing device, setting an initial maximum and an initial minimum threshold values of each channels, and obtaining a reference white and a reference black. Color scale values of each R, G, and B channels are extracted and a minimum, a maximum, and an average values of the color scale values corresponding to each channels are obtained. A modulation factor of each channel is defined by using above defined three values, according to the modulation factor of each channels to re-define a new maximum threshold value as a reference white and a new minimum threshold value as a reference black. According to the obtained reference black and the reference white to complete the white balance adjustment of the image.