Gas concentration measuring system and measuring method

The invention discloses a gas concentration measuring system which comprises a light intensity sinusoidal variation laser generating module, a pulse laser and continuous laser generating module, a double-fiber collimator and a signal processing module, the light intensity sinusoidal variation laser generating module generates light intensity sinusoidal variation laser with the same absorption wavelength as the to-be-detected gas, and the light intensity sinusoidal variation laser is emitted into the to-be-detected gas through the double-fiber collimator to form gas refractive index change; the pulse laser and continuous laser generation module generates a path of pulse laser which is far away from the absorption wavelength of the gas to be detected, and the pulse laser is emitted into the gas to be detected through the double-fiber collimator to generate stimulated Brillouin scattered light; the pulse laser and continuous laser generation module generates another path of continuous laser of which the frequenc