A controllable transmission system and a method thereof are provided. The controllable transmission system includes a first rotation device, a coupling device and a control device. The first rotation device includes a transmission shaft, a rotation body and a plurality of blade units connected with the rotation body, wherein each of the blade units includes an adjustable blade having a first and a second contact elements and having an opening corresponding to the adjustable blade. The coupling device is mounted beside the rotation device and includes a coupling unit having a first and a second contact surfaces. The control device is connected with the coupling device for controlling a movement of the coupling device to cause one of the contact surfaces positioned corresponding to a respective one of the first contact element and the second contact element.