1.6 μm single-frequency lasers have important applications in laser wind lidars, differential absorption lidars, optical communication and pumping optical parametric oscillators. We introduce the main techniques to get single-frequency output in solid-state lasers, including micro-chip cavity, twisted mode cavity, the cavity with F-P etalons inside, traveling wave ring cavity, coupled cavity and the non-planar ring resonator. The research progress of 1.6 μm single-frequency lasers in China and abroad are summarized.