The large specific surface area advantage of low-dimensional nanomaterials greatly improves the reaction efficiency between materials and environmental gas molecules， which plays a crucial role in improving the sensitivity and response speed of the key hydrogen-sensitive devices in fiber optic hydrogen sensors. In this paper， we describe a new method for the preparation of high-performance Au-Pd core-shell nanoparticle monolayer hydrogen-sensitive thin films by self-assembly at the oil-water interface as well as a transmission fiber hydrogen sensor based on the film. In the experiment， spherical Au nuclei with a particle size of approximately 12 nm were prepared via a hydrothermal synthesis method. A Pd growth liquid was then added to the aqueous solution of Au nuclei to obtain Au-Pd core-shell nanoparticles with a particle size of approximately 22 nm. The Au-Pd core-shell nanoparticles were modified by octadecylamine and transferred to a toluene solution using phase transfer technology. Finally， nanoparticle monolayer hydrogen-sensitive films with high coverage and fewer voids were prepared by pulling at the toluene-water interface. Characterization analysis results showed that the size of the Au-Pd core-shell nanoparticles formed was uniform with outstanding crystallinity， and the density coverage rate of the prepared nanoparticle monolayer film was 87%. A transmission fiber optic hydrogen apparatus was built to characterize the hydrogen response characteristics of the prepared Au-Pd core-shell nanoparticle monolayer at different hydrogen concentrations. The experimental results show that the nanoparticle monolayer hydrogen-sensitive thin film exhibits good stability in a number of cycle tests with high hydrogen response speeds （3 s to 4% of hydrogen and 13 s to 0.1% of hydrogen）. The method of preparation of the sensor for rapid and accurate detection of low concentration of hydrogen has a good application prospect.