In order to recognize the output wavelength of fiber swept source prec isely in a wide tuning range,a wavelength calibrating method based on mixed gas absorption lines in mu ltiple near -infrared bands is proposed. Second derivative extremum with segmented threshold and Lorentzian line shape fi tting are used to extract the accurate center positions of multiple absorption lines from mixed gas absorption spectrum.The absorption wavelengths and their corresponding drive voltages can be adopted as stable refe rence points to calibrate the nonlinear characteristics of the fiber Farby-Perot tunable filter.The nonlinear ity is usually described using second order polynomial due to the small fitting error.In this paper,the absorption branch of acetylene in C-band and that of carbon dioxide in L-band are combined to provide wavelength reference.21absor ption lines of acetylene and 16absorption lines of carbon dioxide are selected respectively according to the ab sorption intensity.When the proposed wavelength calibrating method is applied to get the wavelength s of FBG string in C+L band,the standard deviation of wavelength linear fitting in the temperature range from 0℃ to 60℃ is no more than 3.3pm and the linear correlation coefficient is larger than 0.9998.The syst em has a good stab ility with a repeatability standard deviation less than 2.6pm.