Abstract: A high-power high-efficiency narrow-bandwidth thulium-doped fiber laser (TDFL) with output wavelength 1 915 nm was studied in this work. The thulium-doped fiber laser was based on system of master oscillator power amplifier (MOPA). The laser diode with about 40 W output power and 793 nm wavelength was used to pump double cladding large-mode-area (LMA) thulium-doped fiber with 25 m core diameter, the narrow-bandwidth continuous wave(CW) seed laser with wavelength 1 915 nm and maximum power 12.1 W was obtained. When the 793 nm pump power was 142.9 W, after the 8 W seed laser going through the thulium-doped fiber amplifier, the output laser had average power of 90 W, central wavelength of 1 915.051 nm, and the 3 dB spectrum bandwidth was 94 pm, with slope efficiency of 60%, and optical-to-optical conversion efficiency of 63%. The stability of output laser of this system behaves well in the 40 min operation checking time.