The invention discloses a diffuse reflection spectrum analyzer of ultraviolet, visible and near-infrared on-line detection, comprising a housing. A lighting system, a probe, an optical beam splitting system, a signal acquisition system, a correction system and a spectrum processing system are arranged in the housing, wherein the lighting system, the signal acquisition system, the correction system and the spectrum processing system are jointly connected with a power supply system. The lighting system is used for irradiating ray of ultraviolet, visible and near-infrared wave band to light a detected object; the probe is used for collecting the ray of the detected object after diffuse reflection and sends the collected ray to the optical beam splitting system; a grating is utilized to form light of different wavelengths by ray; the signal acquisition system converts the optical signal into a digital signal, and the digital signal is collected; and the spectrum corrected by the correction system is processed, analyzed and displayed by the spectrum processing system so as to determine a detection result. The invention has the advantages of wide application range and accurate measurement.