Blue-green lasers have a broad application prospect in laser display, medical diagnosis, optical data storage, and underwater communication. In particular, the blue-green single-frequency laser has high coherence and can be used in fields such as high-resolution spectroscopy, atomic cooling/capture, and quantum optics, which have attracted extensive attention of scholars at home and abroad and developed rapidly. In this paper, several key technologies of realizing blue-green single-frequency lasers are introduced, such as second harmonic generation (SHG) to obtain blue-green single-frequency lasers, and directly lasing from semiconductor materials. The research status and development direction of the blue-green single-frequency laser are summarized. In addition, according to the research work of our group in the fiber-based blue-green single-frequency laser, the research progress of obtaining blue-green single-frequency lasers through SHG technology based on near-infrared shortwave single-frequency fiber laser is introduced emphatically. Simultaneously, the development of blue-green single-frequency laser technology is prospected.