Fiber-optic gas sensor based on absorption spectra can be achieved on the gas detection accurately,rapidly and highly sensitively.Combined with detection principle and typical system,five optical fiber gas sensing detection methods are summarized in the paper.Single-wave absorption spectrometry detection,differential detection and harmonic detection are develop well,and come to be applied in the oil and chemical industry.The cavity ring-down spectroscopy (CRDS) and active gas cavity detection technology,which is just the rise of novel technology in recent years and has the characteristic that it has a long absorption optical path length and its measure accuracy is independent on the intensity of source,has a great potential for development.