The utility model discloses a pneumatic derailleur selection keeps off actuating mechanism, including driving power source and drive block, the derailleur finger of shifting is connected to the drive block, driving power source provides the drive power of drive block, the drive block both ends respectively with set up the spring that rigidity is the same between the actuating mechanism firmware portion, just the decrement of both ends spring was different when the drive block was in initial position, the drive block with the spring intermediate position sets up the retaining ring, the spring is in compression state always, and works as the spring reachs the decrement is minimum during the retaining ring.