Global warming is becoming more and more serious, and carbon dioxide, as the main component of greenhouse gases, needs to be precisely controlled. Tunable semiconductor laser absorption spectroscopy is widely used in gas detection and other fields due to its high sensitivity and high resolution. In order to further improve the measurement accuracy of the TDLAS system, the denoised TDLAS second harmonic signal was analyzed in the frequency domain on the basis of wavelet denoising, and the frequency domain characteristic signal related to the change of CO2 concentration was extracted by discrete wavelet transform. And establish a regression model to invert the gas concentration. The correlation coefficients of the time domain regression model calibration set and prediction set are 0. 998 5 and 0. 997 3, the root mean square error (RMSE) values were 0. 045 9% and 0. 017 9%, respectively, and the maximum relative error of the prediction set is 4. 62%. The correlation coefficients of the frequency domain regression model calibration set and prediction set were 0. 999 3 and 0. 999 7, the RMSE values were 0. 032 0% and 0. 006 9%, respectively, and the maximum relative error of the prediction set was 1. 54%. The experiment results show that the prediction ability and measurement accuracy of the TDLAS system were effectively improved, which verifies the feasibility of the method.