Due to the failure of traditional oscillation mechanism based on an acoustic wave feedback loop and the supersonic spillage at the duct entrance, the unstart flow pattern of hypersonic inlets is quite different from that of traditional supersonic inlets. What′s more, the hypersonic inlet unstart is more harmful, more closely coupled with the combustor, and has more demand for real time control. Therefore, it should be drawn more attention in the development of hypersonic technology. In this paper, the main progress of the hypersonic inlet unstart is reviewed from its characteristics, classification, detection and control methods. The remaining problems are also analyzed and some issues for future study are suggested.