A 20 nanometer palladium-silver (Pd/Ag) ultra-thin film was used for hydrogen gas sensing. The atomic ratio of Pd: Ag was 3:1, the thin film was evaporated on the optical glass, the Pd/Ag alloy could increase the life and provide the stability of the sensing film. The artificial neutral network was used for processing the data collected from the optical fiber bundle hydro-gen sensor, which could enhance the measuring accuracy, at the same time, the intrinsic and extrinsic influences were eliminated mainly. Experimental results and numerical simulation show the training method available, a linear precision of 0.1% for the optical hydrogen sensor is achieved.