A supporting frame comprises four transversal supporting tubes, each of the transversal supporting tubes having two hollow ends; each two adjacent inner faces of each transversal supporting tube being formed with a screw hole; four longitudinal supporting tubes, each upper end of the longitudinal supporting tubes being a hollow end; moreover, each two adjacent inner faces of each longitudinal supporting tube being formed with respective screw holes; and a plurality of three-way internal connecting units; each three-way internal connecting unit having three inserting ends; each inserting end of the three-way internal connecting unit can be inserted into the hollow ends of the transversal supporting tube and the longitudinal supporting tube; thus by the longitudinal supporting tubes, the four transversal supporting tubes can be assembled as a rectangular upper frame and the four longitudinal supporting tubes being assembled as legs of the upper frame.