Abstract: A multi-wavelength thulium-doped actively mode-locked fiber laser was introduced, in which the gain medium was a 2 m thulium-doped fiber, and the active mode-locking could be realized by LiNbO₃ intensity modulator. An optical filter based on birefringence was added into cavity, the birefringence filter effect of polarization maintaining fiber was used to filter out the superfluous supermode noise in cavity, and also the multi-wavelength output could be realized. The mode-locked pulse frequency spectrum signal-to-noise ratio could reach to 68.48 dB at fundamental frequency, and the maximum number of wavelength channels was 5 in a stable mode-locked state. Furthermore, the polarization independent isolator in cavity was replaced by polarization dependent isolator, and mode-locked pulse was modulated by digital signal. The optical signal-to-noise ratio of eye diagram can be increased by 8.67 dB, which indicates that time stability of mode-locked pulse can be improved effectively.