The invention discloses a high-resolution micro broad-spectrum reflective optical system for a spectrograph, which relates to the field of optical analytical instruments and solves the problems of low spectral resolution capacity, low optical energy transfer efficiency and complex instrument processing, installation and debugging of the instrument having the conventional optical system. The system of the invention comprises an optical fiber interface, a slit, a collimator objective, an imaging objective, a detector image surface, a planar reflection grating and a rotating platform, wherein the planar reflection grating is arranged on the rotating platform, a sample light source is coupled to the optical fiber interface and projected into the collimator objective from the slit; the parallel light beam emitted by the light source and transmitted out from the collimator objective is projected to the planar reflection grating and reflected to the imaging objective; the light beam transmitted out from the imaging objective is imaged onto the detector image surface to form an image signal, and the spectral absorption components of the sample light source can be analyzed; and the collimator objective and the imaging objective are spherical reflector. The system can be widely used in portable spectrograph for field geological and hydrologic survey and military reconnaissance.