Abstract: In the analyses of severe accidents of nuclear power plants, it is very important to study molten-fuel-coolant-interactions. In the paper, the motion images of molten stannum in water and the pressure wave were obtained in different conditions, which are different temperatures of the molten stannum, different temperatures of the water and different diameters of the molten stannum, by using the high-speed camcorder and the pressure sensor. Furthermore, the process of the interactions was considered.