A dual-wavelength fiber laser with a narrow bandwidth, based on a high finesse fiber ring filter has been proposed. Polarization-maintaining fiber Bragg grating（PM-FBG） and a high finesse fiber ring filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device to produce dual-wavelength. The fiber ring filter consists of two optical couplers and a section of weak pumped erbium-doped fiber(EDF). Because of the delay of cavity length and the gain generated by the EDF, the filter has spectral response with a high finesse. The incorporation of the fiber ring filter leads to the suppression of undesirable mode and makes the output laser narrow bandwidth. Under 980 nm LD pumped, the maximum outputs of the two wavelengths are 5.27 mW and 1.02 mW, respectively, at the room temperature. And the wavelength spaces of the two wavelengths are tunable within the range between 0.16 nm and 0.32 nm.