The motion of debris flows can be depicted in the following manner:1. Debris flows consist of the neunrally suspended load, the suspended load and the bed load. The fine particles (silt and clay in general and including sand for debris flows with heavy concentration), called as "neutrally suspended load" in this article, mix thoroughly with water and form the liquid phase-------the slurry which behaves as a Binghamfluid. The coarse particles in turbulent debris flows move as suspended load and bed load, and assume the form of bed load in quasi-viscous and viscous debris flows. Both the suspended load and the bed load form the solid phase of the flow.