The invention relates to a tunable narrow-linewidth fiber laser based on an interval tunable phase shift fiber gratings. The tunable narrow-linewidth fiber laser based on the interval tunable phase shift fiber gratings comprises a laser device (LD), a WDM coupler, an erbium-doped fiber loop, an optical isolator, a circulator, the fiber gratings, a phrase shift fiber grating tuner, an optical coupler, a wavelength meter, an input and control circuit and an output optical coupler, wherein the WDM coupler, an erbium-doped fiber, the optical isolator, the circulator, the phrase shift fiber grating tuner and the optical coupler form an loop cavity; the circulator, the fiber gratings and the phrase shift fiber grating tuner form an adjustable filter inside the cavity. Phase shift amount of the phrase shift fiber gratings is changed by changing the length of an air gap between the two fiber gratings so that tuning of output laser wavelength can be achieved. According to the tunable narrow-linewidth fiber laser based on the interval tunable phase shift fiber gratings, the tunable phase shift fiber gratings, the optical coupler, the wavelength meter, the input and control circuit and the output optical coupler form an input and feedback control loop, the needed laser wavelength is obtained through feedback control, and stability of the laser output wavelength is ensured.