The utility model provides a be used for 30MW to fire press group flame cylinder base circle inner arc hole graduation instrument, the utility model relates to a be used for 30MW to fire press group flame cylinder base circle inner arc hole graduation instrument, the utility model discloses a machining precision is low when solving among the prior art 2 hole through -holes of flame cylinder base circle processing phi, 2 spot facing work fashion cards of phi difficulty, and process the problem that work efficiency is low in hole, the on -off device comprises a base, the guide rail, positioning pin, the slider, first hex bolts, the locating piece, the round pin axle, the gasket, pressing plates, adjusting shim, two adjusting screw, two cylindric locks, two stud, two hexagon nut, two stoppers, three voussoir, a plurality of hexagon socket head cap screw and a plurality of second hex bolts, the utility model belongs to the machining field, an.