The invention relates to a computing method of a white balance correct value. The computing method comprises the following steps: using fill light to capture an image by an image-capturing device; providing a brightness ratio of the current environmental light and the fill light to the image and obtaining image color proportions influenced by various light source color temperatures; neutralizing the two proportions of the light source color temperatures to obtain the white balance correct value; and finally, correcting the white balance of the image by the white balance correct value.