The invention discloses a single-frequency narrow-band optical fiber laser based on a high roundness three-dimensional rotational symmetric microcavity. The laser comprises a semiconductor laser pumping source, a wavelength division multiplexer, an optical isolator, a rare earth doped fiber, a polarization controller, an optical coupler and a high roundness microballoon cavity-conical fiber coupling unit. The semiconductor laser pumping source is connected with the optical isolator through the wavelength division multiplexer, and is connected with the rare earth doped fiber through the output end of the optical isolator. The output end of the rare earth doped fiber passes through the polarization controller, the high roundness microballoon cavity-conical fiber coupling unit and the optical coupler in order, and finally is connected with the input end of the wavelength division multiplexer through the output end of the optical coupler to form a closed cavity. According to the invention, high roundness microballoon cavity-conical fiber coupling unit is used to select the frequency; through ultra-narrow bandwidth echo wall mold resonance spectrum formed in the high roundness microballoon cavity, the output laser has the advantages of ultra-narrow bandwidth; and the laser has the advantages of great coherence, high stability, compact structure, low cost, small loss and the like.