Abstract: The transmission light in the hollow-core optical fibers will interact with the gas molecules for a long distance with a high energy density, to provide a high-performance platform for the spectroscopic gas sensing. This paper reviews our studies of the trace ammonia gas sensing based on the hollow fiber Fabry-Perot interferometer and the photothermal spectroscopy. The phase change of the transmitted light in the hollow-core optical fibers with the photothermal effect of the gas is measured for the sensing of the absorptive gas’s concentration. Using a hollow photonic bandgap fiber of 4 cm in length as the gas sensing probe, a photothermal interference gas sensing system in the near infrared band is constructed. A trace ammonia gas sensing system with an equivalent noise concentration of 4.93 ppmv (corresponding to an absorption coefficient of about 3.3×10^-7 cm^-1) and a resolution of 39 pm between absorption peaks of ammonia are implemented. This optical fiber photothermal interferometry gas sensing technology has a series of inherent advantages of the spectroscopy technology, which ensures application potentials in the aerospace field such as the leakage detection, and the gas component analysis.