High-precision and rapid monitoring of hydrogen concentration is of g r eat significance in many fields.In this paper,a long-period fiber grating hyd r ogen concentration sensor based on Pd/WO_3film is proposed.First,the hydrogen sensing characteristics of Pd/WO_3film-coated LPFG are studied.The optical si mu lation software is used to simulate the sensing conditions of the film with a re fractive index in the range of 1.99－2.0.The simulation results show that when t he hydrogen concentration increases,Pd/WO_3film When the refractive index decr eases,the resonance wavelength of the LPFG transmission spectrum is blue shifted ,and the sensitivity of the resonance wavelength shift to the refractive index change of the Pd/WO_3film is 256.9nm/RIU.In order to enhance the sensitivity of the coated LPFG hydrogen sensor,the effect of the cladding radius and period on the resonance wavelength sensitivity was further studied.The results show th at the LPFG resonance wavelength sensitivity increases with the increase of the period Λ;under the same period,the cladding The smaller the radius,the larg er the offset value of the resonant wavelength.This research has important guidi ng significance for the development of highly sensitive and reusable fiber optic hydrogen sensors.