A dual-wavelength tunable spacing all fiber thulium-doped laser is reported and demonstrated.The conventional ring cavity is used in this fiber laser, 1 565 nm pump source can achieve maximum output power 33 dBm, and a segment of 4m long single mode thulium-doped fiber is gain medium.The filter is a composite structure based on multimode interference effect and Sagnac ring. Through the composite filter, it can radiate tunable spacing and high side mode suppression ratiodual- wavelength laser output. The experimental results suggest that not only dual-wavelength tunable spacing from 3 nm to 80 nm, but also SMSR is 60 dB under the controlling of pump power and polarization controller in composite filter，line-width is 0.2 nm ，power fluctuation is ±1.5 dB/h，bimodal energy difference is less than 4 dBm.