Abstract: The microstructure of the alloy specimens which were melted with the impure uranium and pure uranium respectively,and their hydrided specimens were analyzed by OM and SEM,moreover,the composition of the hydrided specimens were studied by SEM-EDS.The results showed that the contents of impurity elements of Fe and C were both higher in the impure uranium-contained specimen than in the pure uranium-contained specimen,in which the elements were more homogenously distributed in the zirconium hydride matrix.There was great difference of expansion coefficient between the precipitate which consisted of the elements of U,C,a little Fe and zirconium matrix in the impure uranium-contained hydrided specimen,thus when the volume of zirconium matrix increased due to absorbing hydrogen,the precipitate as a secondary phase pinned in the matrix so that the stress was concentrated resulting in the hydrided specimen cracking.In the pure uranium-contained hydrided specimen,the elements of U and C which existed in the form of zirconium carbide relatively homogenously distributed in the zirconium hydride matrix,and the stress in the hydrided specimen did not concentrate so that the hydrided specimen did not cracked.