A combined tool for a screw tap lengthening bar comprises a sleeve, the lengthening bar and a pull lever, wherein the sleeve comprises a first end surface and a second end surface which are opposite to each other, a first deep hole allowing a screw tap mounting end to be inserted is formed in the first end surface, and a second deep hole is formed in the second end surface; a first end of the lengthening bar is inserted in the second deep hole; and the pull lever is in a rod shape, a mounting hole is formed in the pull lever, and a second end of the lengthening bar is inserted in the mounting hole, so that the pull lever can drive the lengthening bar to rotate. The tool is simple in structure, the sleeve can form multiple dimensions for selection, a screw tap is convenient to replace and mount, the tool is high in practicability, and the screw tap does not fall easily.