The invention discloses a special tool for special-shaped nut turning. The special tool comprises a positioning shaft (1), a support block (2) and a pin (4), and is characterized in that the support block (2) is sleeved with the positioning shaft (1) through a connecting bolt (3) and the pin (4); a pressing screw A (5) and a pressing screw B (6) are mounted in bolt holes formed in the side surfaceof the support block (2); and a special-shaped nut (7) is clamped in the positioning shaft (1) by the pressing screw A (5) and the pressing screw B (6). The special tool is short in machining time, high in efficiency and excellent in quality.