In order to describe quantitatively the fatigue characteristic of the alloy Zr-4’s low-cycle fatigue fracture (Zircaloy-4), based on wavelet decomposition technology, the change of fracture energy in 3D space and the effect of sample state and loading direction to fatigue life were studied. The obvious stages of energy curve were discovered along the crack expanding direction in the propagation zone. There were large changes in the 3D appearance of fatigue fracture along the crack expanding direction. The most roughness segment is in the primary stage, and then the 3D appearance of fatigue fracture was becoming smoother. The energy of crack was far larger than that of the ambient body in vertical direction of the crack propagation. It was showed that the 3D appearance of crack is steeper than that of ambient areas. The energy curve of hydrogenation is above the curve of hydrogen free in the same loading direction. Therefore, hydrogen can improve the fatigue characteristic of Zircaloy-4. According to energy curve, low cycle fatigue life of R sample is larger than that of T sample. However, the result of experiment isn’t coincident. It showed that there is a definite localization to differentiate the fracture life only using energy curve.
