The invention discloses a narrow-band fiber laser for mixed medium whisper gallery mode microcavity full-optical tuning. The fiber laser comprises a semiconductor laser pump source, a wavelength division multiplexer, a gain fiber, a fiber isolator, an optical coupler, a polarization controller and a tapering fiber coupling mixed medium microcavity, wherein the units are connected end to end in a fiber coupling manner to form a fiber resonant cavity in a closed manner. The tapering fiber coupling mixed medium microcavity is taken as a mode selection unit in the fiber resonant cavity, light is coupled into the microcavity through one end of a tapering fiber, total reflection transmission is carried out on each end face to form a whisper gallery resonance mode, and the light is returned to the fiber resonant cavity through the other end of the tapering fiber. The mixed medium microcavity is composed of two or more than two layers of media, namely one or more layers of medium films with high index of refraction, great thermo-optical coefficient and high light transmissivity are wrapped on the inner layer medium surface of the microcavity. The laser has the characteristics of large wavelength coverage full-optical tenability, compact strucutre, good monochromaticity and the like.