We　demonstrated　a　narrow-linewidth　Ho:yttrium　aluminum　garnet　(YAG)　injection-locked　laser　by　using　a　1908　nm　thulium-doped　fiber　laser　as　a　pumping　source　to　generate　2.09　mu　m　single-frequency　pulses.　A　compact　single-longitudinal-mode　nonplanar　ring　oscillator　(NPRO)　based　on　Ho:YAG　material　with　a　beam　quality　factor　of　1.01　at　the　central　wavelength　of　2090.91　nm　was　considered　as　the　seed　source.　In　the　experiment,　the　pulse　energy　of　3.6　mJ　with　a　pulse　width　of　161.6　ns　from　single-frequency　Ho　laser　was　achieved　at　a　pulse　repetition　frequency　(PRF)　of　100　Hz.　The　linewidth　of　the　single-frequency　pulse　spectrum　monitored　through　the　heterodyne　method　was　approximately　1.9　MHz　at　the　lowest　Ho　laser　energy.