Abstract: The phase compositions of zircaloy changing in hydrogenation and dehydrogenation process were analyzed by XRD.The microstructure was observed by metallographic.The results show that the phase compositions of zircaloy changing in the two process are same.The microstructures changing in the two process is only different in α+δ+γ three phase zone.The network-like distribution phase changing in the hydrogenation progress is more significant than that in the dehydrogenation process.In the rest phase zone,the hydrogen content determines the microstructures of zirconium hydride.The main reason for this phenomenon is that the hydrogen diffusion mode in the hydrogenation is different to that in the dehydrogenation process.The hydrogen diffusion in the hydrogenation progress is controlled by the grain boundary diffusion,and the hydrogen diffusion in the dehydrogenation progress is controlled by the crystal diffusion.