The invention relates to a DLP technology and compressive sensing theory-based ultra-sensitive spectrum detection method and system. According to the detection method, with DLP light splitting technologies and a compressive sensing theory adopted as a core; a single-point detector is adopted, and the DLP light splitting technologies are used in combination, the ultra-sensitive spectrum detection can be realized through adopting the compressive sensing theory. The ultra-sensitive spectrum detection system includes an optical filter / optical filtering system 1, a lens 2, a slit 3, a collimating / focusing mirror 4, an optical grating 5, a DMD device 6, a single-point detector 7 and electric control system and software 8. The sensitivity of the ultra-sensitive spectrum detection system can be significantly increased, and the cost of the ultra-sensitive spectrum detection system can be decreased manyfold. The system can be widely applied to spectrograph systems using optical grating light splitting, such as Raman spectrographs, infrared spectrographs, fluorescence spectrographs and SPR spectrographs.