An automatic method of setting a desktop background is provided. The automatic method of setting a desktop background is applied to an electronic device which is combined with a protective cover, wherein the protective cover has a conducting area corresponding to a specific shape, location or area. The method includes the following steps of receiving protective cover information generated by a touch screen of the electronic device touching the conducting area of the protective cover; determining whether the protective cover information is in accordance with one of a plurality of preset protective cover information; and setting desktop background displayed by the touch screen according the preset protective cover information when the protective cover information is in accordance with one of the plurality of preset protective cover information.