The invention relates to a self-control intramedullary bone prolong device, which is formed by left fixing end (1), left connecting sheath (3), motor (4), motor support (5), copper sheath (60, guide key (7), outer cylinder (8), inner cylinder (9), central screw (10), and right fixing end (12). When in surgery, it can be planted into intramedullary to connect the bone with pin; when the motor rotates, the central screw rotates to axially move the inner cylinder to prolong the bone; when the motor stops, the device is stopped to fix the bone; when the motor rotates reversely, it can contract the bone. The invention has little hurt on human, while its length can be adjusted and the minimum drawn length in one time is 0.1mm.