A gas analysis system. The system includes a Fourier transform infrared (FTIR) spectrometer, a signal transformation module, an unknown chemical analysis module, a calibration model determination module, and a gas concentration calculation module. The signal transformation module receives electronic signals corresponding respectively to background and sample interferograms corresponding to a sample gas from the FTIR spectrometer for further calculation to obtain an absorption spectrum of the sample gas. The unknown chemical analysis module qualitatively analyzes the absorption spectrum of the sample gas to determine the chemical species in the sample gas. The calibration model determination module decides a calibration model. The gas concentration calculation module calculates the gas concentration of each chemical species according to the absorption spectrum, the calibration model and a standard spectrum of the chemical species.