Because of the advantages of high selectivity, high resolution and fast speed, the tunable diode laser absorption spectroscopy(TDLAS) technology is widely used in such aspects as environmental testing and industrial process testing. The Lorentz linetype fitting, the principle and implementation steps of Levenberg-Marquardt algorithm, and the realization researches of Lorentz linetype fitting of absorption lines based on Levenberg-Marquardt algorithm are investigated. After concentration inversion of six group different concentrations of CO2 standard gas, the correlation coefficient between inversion concentration and the actual concentration is 0.9928. The result shows that Lorentz linetype fitting can invert gas concentration accurately, which has practical guiding significance for concentration inversion in the TDLAS technology.