In order to measure the absorption spectrum accurately and reduce the influence of temperature and turbulence fluctuation on spectral measurement, the method of spectrum simulation and 20kHz high frequency scanning was adopted. The low temperature sensitivity line P(10) in mid-infrared fundamental frequency transition band was selected. The data of absorption spectra and volume fraction of engine CO with the change of time were obtained. The theoretical analysis and experimental verification were carried out. The results show that, the influence of target gas temperature change on volume fraction can be reduced by 48.28% within the scanning range of P branch line. The range of variation is (153±123)×10-6. The scheme can provide a high-speed, accurate and real-time monitoring scheme for CO laser remote sensing measurement of engine exhaust.