In order to obtain a high sensitivity and stability to hydrogen,an optical fiber sensor based on palladium-yttrium (PdY) allog nano-film is designed and fabri cated in this paper.A cleaning process was used to wash a substrate of quartz gl ass and targets to obtaine good binding performance between film and basement.Th e 55nm thick PdY film was deposited on the substrate by the double-target reac tive magnetron co-sputterng,in which the atom content of yttrium is 10%.And a 5nm-thick pure palladium protective layer was deposited on the film at last to prevent it from oxidation.The reflective optical fiber bundle sensor system with a single light source and double light paths was designed and realized.The info rmation containing hydrogen concentration was extracted through a division opera tion between the testing light path and the reference one.This sensor system was tested by standard gas and dry air.The results show that it exhibits long time stability to dry air and has response time of 343s,266s and 187s to 1.5%,3.0% and 4.0% hydrogen,respectively.Although the sensor has zero drift to the standa rd gas at different degrees.it shows strong stability and repeatability in respo nse value and increment of zero after three or four cycles of test.