A resolution adjustment method applied to image display of a display device includes the display device providing a display menu to obtain a display layout composed of a plurality of display areas, the display device performing a resolution parameter setting on each display area according to the display layout and an original resolution parameter of the display device, the display device generating an updated product code and a plurality of updated resolution parameters according to an original product code and the original resolution parameter of the display device and each resolution parameter setting, and each image source reading the updated product code and the updated resolution parameter and outputting an image corresponding to the updated resolution parameter via a corresponding transmission port to the corresponding display area.