Abstract: The debris flow is a common natural disaster in the mountainous regions. It is a special two-phase fluid. In general, there are two types of debris flows: low-viscous debris flow (where collision and energy dissipation are dominated) and viscous debris flow (where viscosity is dominated) . In this paper, the formation, the classification and the dynamics of debris flow are discussed, some urgent problems are pinpointed, which include the theory of confluent flow and the law of fluid resistance. It is predic...