When high-precision laser absorption spectroscopy techniques such as cavity ring-down spectroscopy and cavity enhanced spectroscopy are used in gas measurements, the stability of laser output wavelength directly affects the accuracy of measurement results. Therefore, accurate measurement of laser wavelength is crucial to high-sensitivity laser absorption spectroscopy technology. Taking the distributed feedback (DFB) laser commonly used in the cavity ring-down absorption spectrum as an application example, a wavelength monitoring system is built in this work based on Fabry-Perot (F-P) etalon. The system utilizes the interference phenomenon of F-P etalon, and adjusts the laser driving current to scan the wavelength. And at the same time, a standared wavelength meter is used as reference, then the functional relationship between wavelength and interference light intensity can be obtained, which will be used for inversion of wavelength information in the subsequent measurement. In the experiment, a DFB laser with central wavelength of 1653 nm is used, and the F-P system has realized the wavelength measurement in the range of 1653.66160 nm to 1653.77718 nm for this laser. The linear fitting correlation between the measurement results and the reading of the reference wavelength meter is 0.9999, which proves the reliability of the F-P wavelength monitoring system. In order to further verify the stability and measurement accuracy of the system, a 10-minute continuous monitoring is carried out at the central wavelength of the laser, and the results show that the system accuracy is ± 9.12 × 10^-5 nm. It is indicated that this work is of great significance for realizing high-precision atmospheric background and isotope gas measurement by cavity ring-down absorption spectroscopy technology in the future.