A fiber grating demodulation system for enhancing spectral resolution by finely adjusting an imaging focus mirror, includes a laser pump source, a wavelength division multiplexer, a fiber Bragg grating, a diaphragm, a slit, a collimating mirror, a light splitting grating, an imaging focus mirror, a linear array detector. The laser pump source, the wavelength division multiplexer, the fiber Bragg grating are connected in sequence, the wavelength division multiplexer is connected to the diaphragm. Light emitted from the laser pump source is multiplexed by the wavelength division multiplexer and then enters the fiber Bragg grating, a reflection spectrum of the fiber Bragg grating enters the slit of the fiber grating demodulation system as injected light. After passing through the slit, the injected light is reflected by the collimating mirror, the light splitting grating, and the imaging focus mirror in sequence, and is finally converged to the linear array detector.