We demonstrate a tunable erbium-doped fiber ring laser based on an all-fiber filter. The filter consists of an optical
circulator, a fiber loop mirror(FLM) and a polarizer which is spliced to a segment of polarization maintaining fiber (PMF)
at the angle of 45° with respect to the fast axis of the PMF. The laser can be tuned by adjusting two polarization
controllers (PC) in the laser. The tuning range can reach to 6.08nm (1553.92-1560.1nm) with side mode suppression
ratio (SMSR) over 38 dB. The stability of the laser is verified at room temperature in one hour, and the power fluctuation of the laser is less than 0.5 dB.