The invention provides a stent delivering system and a handle assembly thereof. Through the internal structure of the handle assembly, and connection structures between the handle assembly and other parts of the stent delivering system, and the stent releasing structure and the whole support delivering system are more reliable; and the handle assembly controls an external tube, a covered cannula assembly and a back releasing assembly to successively perform releasing motions, and then a gradual releasing process of covered cannula releasing-stent primary releasing-stent complete releasing can be achieved. The stent releasing accuracy of the stent delivering system can be improved, and medical accidents can be reduced.