The invention provides an image addition processing method which comprise the following steps of: setting the transparency of each image layer, wherein the sum of transparency of all image layers is less than or equal to 1; obtaining pixel values, effective values and transparency of pixels of all image layers at the same position; calculating the product sum of the pixel values, effective values and transparency of pixels of all image layers at the same position; and displaying the product sum of all image layers at the same position. The invention provides an image addition processing device which can simultaneously add a plurality of image layers, improve addition processing efficiency of the plurality of image layers and can display the image layers in real time.