The utility model discloses a cylinder booster, include the cylinder connecting piece who is connected with the piston rod, cylinder connecting piece movable mounting is on the support, the cylinder connecting piece end -to -end connection has the slip rack, slip rack and gear engagement, the push rod has set firmly on the gear, crank link mechanism is connected to the push rod, the gear below is provided with fixed rack, and the two meshes mutually, state slip rack, push rod and fixed rack three parallel arrangement. The utility model discloses the realization makes the dynamic property of engine improve greatly under the prerequisite that does not change the engine displacement, perhaps guaranteeing under the unchangeable circumstances of engine power for the cylinder volume reduces, thereby improves fuel economy.