Tunable diode laser absorption spectroscopy （TDLAS） exploits the tunable and narrow linewidth characteristics of a diode laser to improve the selectivity and sensitivity of CO2 measurements in harsh environments， such as those with complex gas components and high temperature. The scanned-wavelength direct absorption spectroscopy technique based on TDLAS is commonly used for gas concentration inversion. However， the absorbance integral method in gas concentration inversion is applied in the frequency domain， which requires a complex system to retrieve accurate frequency-domain information. To avoid this problem， the present paper proposed a new gas-concentration inversion method based on calibration of the direct absorption peak value. First， the theoretical changes of absorption peak value with concentration（10%-20%） and temperature（298-338 K） were analyzed in a numerical model of the target gas （carbon dioxide， CO2）， which was established using the HITRAN2016 spectrum database and referring to high temperature and high concentration CO2 environment in tail flue of the power plant. The theoretical change was used as reference basis for establishing the actual absorption peak value concentration calibration model and temperature correction curve. To verify the feasibility of the method， a custom-built CO2 detection system based on TDLAS was built. The mean squared relative error of the inversed CO2 concentration by peak value calibration method was 1.08%， confirming that the gas-concentration inversion method based on direct absorption peak value calibration can accurately measure high concentrations of CO2.