In order to accurately determine the volume fraction of the gas to be measured and to improve the stability of tunable diode laser absorption spectroscopy (TDLAS)，the scan signal of the TDLAS gas detection system was optimized. Based on the HITRAN database，the absorption peak of methane gas near 1654 nm was selected，and the absorption coefficients of the gas mixture containing methane，water vapor and carbon dioxide were calculated; a visual simulation tool was used to simulate the gas detection system theoretically，and the simulation results were verified by the gas detection system. The results show that the stability of the detection system is improved by optimizing the scanning signal，and the deviation value is reduced from 0.3% to 0.07%; the inverse model of the mean value of the second harmonic signal and the volume fraction of the gas is established，and the correlation coefficient of the linear fit R2=99.99%. This study has a certain reference value for improving the stability and accuracy of the TDLAS system and achieving high stability gas detection.