In order to study the effect of laser modulation parameters on the peak, signal-to-noise ratio, peak width, symmetry, and signal integrity of second harmonic signals, the analysis based on the hardware system and the Simulink analogue model were verified that the theoretical simulation results were consistent with the signal variation trend of the hardware system, and at the same time the optimal modulation parameters of the CO2 detection system were determined. Through the experimental system, the absorption spectra of different volume fraction of CO2 at 1432.04nm were measured, the inversion model of the signal intensity at the main absorption peak and CO2 volume fraction was established, and the system performance and measurement accuracy were analyzed. The results show that the linear fitting coefficient R2 is 0.9998, the maximum relative error of gas volume fraction inversion is 0.7333%, and the detection limit of the system is 0.0074%. The ideal second harmonic signal can be obtained through the optimal selection of modulation parameters, so as to achieve accurate inversion of the gas volume fraction to be measured. The study provides an important reference for the optimization of modulation parameters in the detection system and provides guidance for the improvement of the measurement accuracy of the system.