Abstract: An automatic bone traction device for correction bone deformities is disclosed. The automatic bone traction device can include a main body, a step motor, a series of transmission gears, and connectors. In one implementation, the step motor operates at a speed of eight steps per second, and the series of transmission gears can step down the motion of the step motor to two revolutions per day. The generated driving torque is then transmitted to a bone distractor, such as a commercially available intermittent distractor. The automatic bone traction device is capable of activating the bone distractor continuously at a rate of two revolutions per day. Advantageously, a flexible shaft is used to connect between the transmission gear assembly and the bone distractor. The flexible shaft allows the main body of the bone traction device to be mounted away from the bone distractor at a convenient location for the user.