| Pd-Ag alloy nanoparticle chains were prepared by electrodeposition on the surface of Polyacrylonitrile carbon fibers(PANCF) which were served as the template in this paper. Morphologies and composition of the nanoparticle chains were analysed by SEM, EDX, after that, the relations between the morpholohy and parameter were discussed finally, and a CHI660B electrochemical workstation was applied to detect the performance of hydrogen sensing. The main results were gained as following:(1) PAN-based carbon fibers surface need to be pre-treatment before electrodeposition. The better process of Carbon fibers surface pre-treatment is: degummed for 30-60 min in muffle furnace at 400℃; and coarsened 40～80 min at 40～50℃. Through degumming, degreasing and coarsening process, the carbon fibers showed steps morphology which like highly oriented pyrolytic graphite surface, and the steps were parallel. This morphology is benefit to formation of alloy nanochain arrays.(2) In the potentiostatic three-pulse electrodeposition process, the growth time and growth potential were main factors to effect the alloys composition on nanopaticles surface. Pd-Ag alloys with 16～25% silver content in the alloy can be obtained in the electrolyte of 0.5 mmol·dm-3 Pd(NO3)2+0.033 mmol·dm-3 AgNO3+2 mol·dm-3 NH4NO3 when growth for more than 200 s under the growth potential of-0.25～-0.45 V.(3) Pd alloy nanoparticle chains were affected directly by the nuclear potential and time. If nuclear potential of -1.0～-1.5 V was controlled for 10～50 ms, the nanoparticle chains could be successfully fabricated.(4) In the electrolyte of 0.5 mmol·dm-3 Pd(NO3)2+0.033 mmol·dm-3 AgNO3+2 mol·dm-3 NH4NO3, Pd-Ag alloy nanoparticle chains can be fabricated on carbon fibers by using constant potential three-pulse electro-deposition:+0.8 V～1.0 Oxidation for 3～5 s,-1.0～-1.5 V nucleation for 5-40 ms and -0.25～-0.35 V growth for 200～300 s. The nanoparticle chains fabricated were well-proportioned in the composition and parallel in the nanostripes. The particles in the chains were between 80～120 nm and the silver content of 16～25% in the surface of nanoparticle chains accord with the sensing requirement.(5) The sensor made of Pd-Ag alloy nanoparticle chains responded to the hydrogen gas of 0.30～5.00%(the volume ratio, V/V) at room temperature. The response time increased with the concentration decreasing sharply below 3.50%. The shortest response time of Pd alloy nanoparticle chains was about 300 s and the sensitivity reached to 31.4%. The response current was linearly proportional to hydrogen concentration in the range between 0.30～2.20%, the current signal was kept constant with the rise of concentration beyond 4.00%. The hydrogen sensor has good reproducibility and stability below 3.50% hydrogen, but the hydrogen sensor needs a long time to restore to the original state beyond 3.50% hydrogen circumstance.(6) The hydrogen action with palladium alloy nanoparticle chains is the mechanism of a solution and diffusion, which is a process of surface chemical adsorption, surface infiltration, diffusion and desorption. When the alloy nanoparticles adsorbed hydrogen, the volume would be expanded, which lead to the decrease in total resistence. However, when hydrogen gas escape away, the alloy would return to their original state and the resistance would increase again.
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