Abstract: In order to investigate the coarse mixing stage mechanism of the vapor explosion,an observable experiment equipment facility for low-temperature molten materials to be dropped into water was designed in this study.In the experiment,molten material jet was injected into water to experimentally obtain the visualized information.The effects of metal temperature,coolant temperature and jet diameter were investigated.The experimental results show that jet dimensionless length L/ D agrees well with the correlation.The jet diameter and coolant temperature have effects on the falling of the jet front while metal temperature hasn’t.