Abstract: Molecular tagging velocimetry is a kind of laser diagnostic technique for flow dis-play and velocity measurements.In this paper,the authors introduced the molecular tagging ve-locimetry in detail by analyzing the technique development of tag creating,tag displaying,and data processing.Several application examples of the velocity measurements of supersonic flow, boundary layer flow and the exhaust gas of engine using OH and NO tagging techniques were lis-ted.The problems that the molecular tagging velocimetry has encountered in industrial applica-tion,such as the background in reaction flow,the strong vibration environment and the optical windows restriction,were discussed and analyzed.