A tunable narrow-linewidth single-frequency linear-polarization laser device comprising a heat sink, a pumping source packaged on the heat sink, a first and second collimating lenses, a laser back cavity mirror, a thermal optical tunable filter, a rare-earth-ion heavily-doped multicomponent glass optical fiber, a super-structure polarization-maintaining fiber grating, a polarization-maintaining optical isolator, a polarization-maintaining optical fiber, and a thermoelectric refrigerating machine. The laser device uses a short and straight single-frequency resonant cavity structure, the heavily-doped and high-gain characteristics of the multicomponent glass optical fiber, a frequency selection role and wavelength tuning function of the thermal optical tunable filter and the superstructure polarization-maintaining fiber grating, and combines a precision temperature adjustment technology, and by means of real-time adjustment of distribution of reflection wavelengths and transmission wavelengths, the laser device changes spectrum peak overlapping positions, so as to implement stable output of wide-tuning-range, extra-narrow-linewidth, high-extinction-ratio and high-output-power continuously tunable single-frequency linear-polarization laser.