Tubing plugging often occurs and brings some difficulties to industrial production. This paper proposes a simple pneumatic impactor which can instantaneously generate great acceleration by a reservoir to shock and smash calcium monohydrate bonding in the tubing inwall. The working principle and the mathematical model of the impactor are introduced in detail. In order to obtain its dynamic characteristic, the simulation is performed. The results show that during the movement of the piston back pressure occurs due to the outlet chamber squeezed by the piston with a high speed, and with inlet pressure increasing positions of the piston with different peak velocities are almost the same. This impactor can be used to unplug tubings in oil or gas well.