The invention discloses a single-longitudinal-mode erbium-doped fiber laser based on a gourd-shaped auxiliary cavity, and belongs to the technical field of laser. The system comprises a 980nm semiconductor laser, a 980 / 1550nm wavelength division multiplexer, erbium-doped fibers A and B, an optical coupler, a fiber Bragg grating, a polarization controller, a polarization beam splitter, the gourd-shaped auxiliary cavity and isolators A, B and C. The 980nm semiconductor laser is used for pumping of the erbium-doped fiber A through the 980 / 1550nm wavelength division multiplexer to generate stimulated radiation light. Under the action of the isolator A and the isolator B, the stimulated radiation light is transmitted in the anticlockwise direction. Under the action of the Er-doped fiber B, thefiber Bragg grating, the polarization controller, the polarization beam splitter and the gourd-shaped auxiliary cavity, the stimulated radiation light is finally transmitted in the cavity in only onestable mode; and the stable transmission mode is outputted through the optical coupler and the isolator C. The fiber laser is novel in concept, is simple in structure, can solves a problem of multi-longitudinal-mode oscillation in an annular cavity Er-doped fiber laser, reduces the line width of the fiber laser, and has a wide application range.