The　research　on　medium-infrared　thulium-doped　fiber　lasers　at　2　μm　wavelength　is　widely　used　in　the　field　of　laser　medical,　eye-safe　radar,　non-metal　material　processing,　and　electro-optical　countermeasure　system,　it　has　an　irreplaceable　role　compared　with　other　wavelength　fiber　lasers.　An　all-fiber　wavelength-tunable　passively　mode-locked　thulium-doped　fiber　laser　is　reported.　This　laser　realizes　picosecond　pulses　and　tunable　wavelength　by　using　a　semiconductor　saturable　absorber　mirror　and　a　high-birefringence　fiber　optical　loop　mirror.　This　high-birefringence　fiber　optical　loop　mirror　consists　of　a　2×2　coupler　with　output　ports　spliced　to　a　high-birefringence　fiber.　The　tunable　picosecond　pulse　laser　output　is　obtained　by　changing　the　temperature　of　the　high-birefringence　fiber　in　a　fiber　optical　loop　mirror.　The　center　wavelength　tunable　range　is　from　1952　to　1967　nm,　the　tuning　width　is　15　nm,　the　repetition　rate　is　29　MHz,　and　the　shortest　pulse　width　is　6　ps.　©　2018,　Chinese　Lasers　Press.　All　right　reserved.