Abstract: Irradiation embrittlement of metals has always been one of the most important concerns in the field of nuclear energy safety. The morphology of fracture surface and reduction in area of safety monitoring specimens in commercial nuclear reactor are usually used to characterize and analyze the embrittlement properties of reactor pressure vessel steel, so as to further ensure the safety of reactors. High-purity aluminum has a small neutron absorption cross section, which can effectively reduce the intensity of gamma rays of neutron irradiation metals, protect the health of experimenters and experimental equipment. It is also the earliest material which has been selected for radiation damage research. Therefore, high-purity aluminum was selected as the research object in this paper. The morphology of fracture surface and reduction in area of high-purity aluminum were studied systematically. The results showed that although the toughness of high-purity aluminum decreases with dose, but the reduction in area decreased first, then increased immediately, and then decreased with dose. The morphology of fracture surface changed from one-dimensional blade and lip to two-dimensional triangle and silver ingot with dose. Moreover, when the morphology of fracture surface transforming from one-dimensional to two-dimensional that an abnormal increase in reduction in area occurred. The theoretical analysis showed that the two-dimensional necking instability in transverse and cross section occurs simultaneously during tensile deformation, and the higher the ratio of Young's modulus to plastic instability stress, the more prone to two-dimensional necking instability. It is speculated that neutron irradiation reduces the Young's modulus of high-purity aluminum, which leads to the transformation of necking instability characteristics and the morphology of fracture surface with dose. Finally, quasi-static tensile experimental, reduction in area and morphology of fracture surface analysis were conducted on four representative metals (pure stannum, pure plumbum, soft OFHC and HR2 steel), and the results further confirmed the correctness of the above theoretical analysis.