A 2 μm band active mode-locked fiber laser with 3m thulium-holmium co-doped fiber as gain medium is reported. According to the cavity length, the fundamental frequency is 12.24 MHz and two MZM modulators are used to obtain pulse sequences and spectrum of different repetition frequencies. When the stable repetition frequency is 489.7 MHz, the signal-to-noise ratio is 62.32 dB and the 3 dB bandwidth is 0.09 nm. A mode-locked pulse carrier of 489.7 Mb/s was obtained by synchronous digital modulation, the signal-to-noise ratio of the measured eye image was 11.1 dB. I.IntroductionIn recent decades, due to the needs of equipment production and the development of science and technology, 2 μm fiber laser has been widely valued and developed especially in the medical, beauty and other fields.[1] The 2 μm band is in the safe band of human eyes, it covers the high