Abstract: A corner joint coupling structure of aluminum extrusion cabinet includes a corner joint, a lengthwise horizontal bar, a widthwise horizontal bar, and a vertical bar. The corner joint forms tenon portions for coupling the lengthwise horizontal bar, the widthwise horizontal bar, and the vertical bar. The lengthwise horizontal bar forms therein an inner-threaded channel and the corner joint forms a through hole corresponding to the inner-threaded channel. A threaded fastening element is receivable through the through hole and is threadingly engageable with the inner-threaded channel. As such, assembling operation of two lateral side panel assemblies of the cabinet is made easy and effortless to allow general consumers to do the assembling by themselves in a noise-free manner.