Through measuring and analyzing the infrared absorption spectrum of carbon monoxide, a kind of carbon monoxide multi-parameter detection system was designed based on the characteristics of ultra-narrow-linewidth laser and the spectrum scanning technology. A ultra-narrow-linewidth tunable semiconductor laser was utilized as light source and carbon monoxide temperature detection was achieved by measuring direct absorption spectra at different temperatures. According to temperature data and the principle of differential absorption concentration detection, carbon monoxide concentration and temperature were obtained simultaneously. With the spectrum scanning technology of ultra-narrow-linewidth laser, the spectra of carbon monoxide near the region of 6 354.179 and 6 383.09 cm-1 at different temperatures were measured, and also analyzed and fitted by Voigt profile. Finally the experiments indicate that the temperature measurement relative error is less than 4% and relative temperature fluctuation is less than 3.5%; the concentration measurement relative error is less than 5%, and the minimum detectable carbon monoxide is 0.05%. The multi-parameter detecting system has advantages of high accuracy and good stability, and can be used in power transformer fault gases on-line monitoring in real time.