Abstract: With the acceleration of industrialization, air pollution monitoring has received widespread attention. In order to realize accurate monitoring of trace gas concentration in industrial process, an on-line monitoring system of the gas concentration was built with tunable diode laser absorption spectroscopy technology (TDLAS) and the visualization interface was completed with LabVIEW as the software development platform. The data processing function and gas concentration inversion algorithm were mainly designed, and the effective fitting range of characteristic absorption spectrum was corrected by the environmental pressure parameters obtained synchronously, so the accuracy of absorbance signal was improved. Then by reading the ambient temperature parameters, the gas absorption line was modified to obtain accurate concentration results. The system was applied to the on-line measurement of ammonia concentration at high temperature, and the result of ammonia concentration at high temperature and different pressure was obtained. The result shows that by the spectrum extraction and correction after the determination of parameters, the maximum calculation deviation of ammonia concentration is 3.96% at 500 K, while the maximum inversion deviation of ammonia concentration without modification of pressure and temperature parameters is 18.81%. The system can precisely retrieve the gas concentration under different environmental parameters (pressure and temperature) and realize accurate real-time on-line measurement of industrial high temperature field gas.