A supporting frame, comprising: 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 hole (31, 32); 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, characterized in that. each three-way internal connecting unit is formed by three rectangular ends 4A, 4B and 4C; each end having a hollow inner space; each two inner faces of the rectangular ends of the three-way internal connecting unit being formed with three holes (41, 42); a plurality of enhancing fixing units; each enhancing fixing unit is formed by two connected lower rectangular sheets which is connected with an angle of 90 degrees therebetween; each upper end of the lower rectangular sheet is extended with an upper rectangular sheet; each of the lower rectangular sheets and upper rectangular sheets has a respective screw hole (521, 511); two parallel sides of each lower rectangular sheets are formed with protruding rims; wherein in assembling, two inner sides of the lower rectangular sheets will adhere to inner faces of each longitudinal supporting tube and upper surfaces of the upper rectangular sheets adhere to lower surfaces of respective transversal supporting tubes; then screws are used to lock the enhancing fixing unit to the respective longitudinal supporting tube and respective transversal supporting tubes by the screw to pass through the screw holes of the longitudinal supporting tube, the transversal supporting tubes and the three-way internal connecting unit. 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 hole (31, 32); 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, characterized in that. each three-way internal connecting unit is formed by three rectangular ends 4A, 4B and 4C; each end having a hollow inner space; each two inner faces of the rectangular ends of the three-way internal connecting unit being formed with three holes (41, 42); a plurality of enhancing fixing units; each enhancing fixing unit is formed by two connected lower rectangular sheets which is connected with an angle of 90 degrees therebetween; each upper end of the lower rectangular sheet is extended with an upper rectangular sheet; each of the lower rectangular sheets and upper rectangular sheets has a respective screw hole (521, 511); two parallel sides of each lower rectangular sheets are formed with protruding rims; wherein in assembling, two inner sides of the lower rectangular sheets will adhere to inner faces of each longitudinal supporting tube and upper surfaces of the upper rectangular sheets adhere to lower surfaces of respective transversal supporting tubes; then screws are used to lock the enhancing fixing unit to the respective longitudinal supporting tube and respective transversal supporting tubes by the screw to pass through the screw holes of the longitudinal supporting tube, the transversal supporting tubes and the three-way internal connecting unit.