As an important branch in the field of distributed optical fiber sensing, optical frequency domain reflectometer (OFDR)has the advantages of high sensitivity and high spatial resolution, and is the research hotspot in the field of distributed optical fiber sensing in recent years. The principle and key technologies of OFDR are introduced and the recent progress of optical frequency domain reflectometer is systematically reviewed from two aspects of high spatial performance and remote frequency domain reflectometer. Then, the latest applications of OFDR in different fields are analyzed and the characteristics of different OFDRs are summarized.