The fast response rate and high sensitivity are the two main aim s of optical fiber hydrogen sensor constantly.In hydrogen environment,the characteristics of the spectrum remain to be known.In this paper,we have designed an in- situ hydrogen- sensitive spectral observation system which is suitable for multi-layer transmi ssion probe.The spectral characteristics of multi-layer film structure un der different concentrations of hydrogen were studied by experiment,and the influence on measurement sta bility of the sensor was discussed when the light wavelength changes,which lay the experimental basis for further i mproving the performance of the sensor.And the experimental results show that the change of l ight source wavelength has remarkable effect on the measurement for the sensor,but wavele ngth scanning can effectively avoid wavelength drift problem of the hydrogen sen sor,to achieve high measurement reliability.