The present invention related to a vital sign sensing system, a vital sign obtaining device, and a disposable device. The vital sign sensing system includes the vital sign obtaining device and the disposable device. The disposable device includes an elasticity stopper and a movable fastener. The vital sign obtaining device includes a protrusion. The movable fastener is assembled on the elasticity stopper so that the elasticity stopper is showed a flexion state. In a first procedure that the disposable device is assembled to the vital sign obtaining device, the movable fastener is uninstalled from the elasticity stopper by the protrusion, and the elasticity stopper is converted from the flexion state to an expansion state so as to prevent the disposable device from being reused in vital sign obtaining device.
