Tunable continuous-wave (CW) thulium-doped fiber lasers at 2μm are characteristics by widely tunable range, narrow linewidth and low noise. These lasers are widely used in the fields of laser lidar, remote sensing, optical communication, spectrum analysis, environmental monitoring, and laser medical system, etc, which have become a hot research topic in the fields of fiber laser technology. In this paper, the basic structures and principles of wavelength-tunable gratings in tunable fiber lasers are described. Main gratings include blazed gratings, volume Bragg gratings and fiber gratings. Then, the research progress of tunable CW thulium-doped fiber lasers based on the gratings at home and abroad is summarized. And the development tendency in the future is also discussed.