2 μm single-frequency pulse laser is the key light source of lidar for the detection of the atmospheric wind field and CO₂ concentration. In the paper, the research progress of the continuous-wave 2 μm single-frequency laser, pulsed high-repetition-frequency laser and pulsed low-repetition-frequency laser are summarized respectively, according to different application requirements. Their technical characteristics are analyzed as well. The development tendency of the pulsed single-frequency 2 μm all-solid-state laser is prospected.