A ring cavity Tm-doped fiber laser system was built based on a 1 550 nm fiber laser. And, its spectral chacteristics were investigated. With 1 550 nm pump, the spontaneous emission of the 1.6 m long Tm-doped fiber covered a spectral range from 1 800-1900 nm with a 3 dB bandwidth bigger than 60 nm. Inserting an isolator into the ring cavity, narrow linewidth output was obtained with a 3 dB linewidth smaller than 0.2 nm centering at around 1 900 nm. Further adding a tunable FP filter, tunable, narrow linewidth laser output was attained. The laser spectrum was tunable from 1 840-1 900 nm with a broad tunable range reaching 60 nm while maintaining a 3 dB linewidth of only 0.07 nm. In addition, a telecommunication FP filter at the 1 550 nm waveband was also exploited in this ring cavity laser system for wavelength tuning. And, a narrow linewidth, broadband tunable laser output in two seperated spectral ranges was also recorded. Together with the 2 000 nm FP laser system, this laser demonstrates a wide tunable range from 1 820-1 915 nm which is consistent with the spontaneous emission spectrum of the Tm-doped fiber.