Limiting structure of locking tool

The utility model relates to the field of cutters, and particularly discloses a limiting structure of a locking tool, which comprises an annular shell capable of horizontally sleeving the outer wall of an angle head, the annular shell is fixed on an external machine tool, an annular groove with an opening facing the circle center is formed in the inner wall of the annular shell, and a circle of air bag is arranged along the inner wall of the annular groove. The air bag is communicated with an external air source through a flexible pipeline penetrating through the shell, a plurality of box holding pieces are arranged on the inner periphery, close to the circle center, of the air bag in the annular groove, a spring is connected between the opposite ends of the box holding pieces, the spring is in a stretching state in a natural state, and key grooves facing the circle center are formed in the top faces of the box holding pieces. Convex keys which are matched with the key grooves and also face the circle center