A tunable multi-wavelength Tm3+-doped ring fiber laser based on all-fiber Mach-Zehnder (M-Z) interferometer was designed. The Mach-Zehnder fiber filter consisted of two cascaded 2×2 3 dB couplers,and it connected to the ring cavity through a fiber coupler and reflecting filter was realized by a Sagnac fiber mirror. In experiment,a fiber laser at 1573 nm with a output power of 250 mW was used as pump source,and the pump laser was injected into a segment of 4 m single-mode Tm3+-doped fiber through a 1570/2000 nm wavelength division multiplexer (WDM),and then optical gain at 2 μm band was obtained. A polarization controller (PC) was used for adjusting laser polarization loss in the cavity. By observing tunable multi-wavelength laser around 2 μm band,3 wavelengths were obtained by adjusting the PC.