A wire stretching device for applying a drag force onto a wire wound around an object is provided. The wire stretching device comprises a primary platform, a first sub-platform, a second sub-platform and a driving device. The primary platform comprises a plate, a fixed stick and a track, wherein the fixed stick and the track are disposed on a surface of the plate, and the fixed stick has a first fixing device for fixing a first end of the wire. The object is fixed on a first stage of the first sub-platform, and a second fixing device is disposed on a second stage of the second sub-platform for fixing the second end of the wire. The second sub-platform is moved by the driving device for adjusting the tension of the wire. The first sub-platform is passively moved along the track corresponding to the tension of the wire.