Pulsed laser deposition is a potential preparation method for optical fiber hydrogen sensor. Pd/Ag thin films are prepared through pulsed laser deposition at a low temperature by excimer laser. It is found that Pd/Ag thin films with fine crystal structure are obtained under high pulse laser energy at low temperature by X-ray diffraction (XRD) and atomic force microscope (AFM) methods. The F-P sensor is packaged in a casing structure that can limit the expansion direction of Pd/Ag thin films which absorbs hydrogen. Hydrogen sensing probe is made to test the hydrogen sensing properties of Pd/Ag thin films for the characteristic that the expansion of Pd/Ag thin films which absorbs hydrogen can lead to the change of the F-P cavity. Experiment results show that the sensor can be used to detect the changes of the hydrogen concentration.