Abstract: The melting process of fuel elements is the crucial link of severe accidents. The phenomenon of melting of fuel rods and migration of molten materials involves complex physical and chemical transformation and they are coupled with great uncertainty and are difficult to predict accurately. Therefore, it is necessary to use advanced experimental method to conduct research to investigate the mechanism and behavior characteristics of the melting of fuel rods and migration of molten materials. In order to obtain key experimental data in the process of nuclear reactor fuel rod melting and the molten materials migration, the FROMA (fuel rod melting progression apparatus) was established and a series of experiments were carried out under low temperature. The experiments were carried out using zinc-aluminum structure fuel rods which focused on a series of key phenomena such as the possible damage and melting of fuel rods in severe accidents. The transient axial temperature distribution characteristics of the fuel rod cladding and the dynamic process images of melt expansion, migration and relocation during a severe accident were obtained. Based on the experimental data, an in-depth analysis of the physical phenomena and processes related to the flow, expansion, solidification and migration of the melt were conducted and the dynamic process law of the melt’s expansion and migration in the reactor during an accident was obtained. Rod melting and the flow, expansion, solidification and melting mechanism of the melt in the interstitial channels of the rod bundle were also revealed. The research results in this paper reduce the uncertainty of the existing severe accident analysis procedures and fill the insufficiency of domestic research on the severe accident of the fuel rod melting. The main conclusions are as follows. 1) The melting process can be divided into three parts: heating, melting and disintegration under the low heating power in the low temperature experiments. During the melting process, the test rod will appear some obvious phenomenon such as bubbling, cladding collapse, deformation displacement and molten materials drop. 2) FROMA can visualize the process of cladding bubbling, rupture and core material melting, migration and relocation. 3) Dynamic image parameters, temperature, power and droplet size are obtained in the experiment and it can be used for the preliminary verification and optimization of models in some programs such as MELCOR, MPS, and ABAQUS-FUEL. The experimental research will help reveal the mechanism of the key phenomena during severe accidents and reduce the uncertainty of existing severe accident analysis programs. It can also provide key data support for China’s independent development of related physical models. The date can be finally applied to the preliminary verification and optimization of the models which can be used to analysis nuclear reactor’s design and safety and it’s also significant for engineering application.