Abstract: The main difference between resistances of subaqueous debris flows and the subaerial debris flows are the intermingling and shearing resistances acted on the surface of debris flows.By a series of experiments on the subaqueous debris flows and subaerial debris flows, we can get the velocity ratio of subaqueous debris flows and subaerial debris flows at the same condit ions.The characteristics of debris flow, such as the yield stress, are strongly affecting the velocity relationship of subaqueous debris flows and subaerial debris flows.An equation on the velocity relationship of subaqueous debris flows and subaerial debris flows is given based on the dimensionless yield stress and density of debris flows by non hydroplaning subaqueous debris flows experiments.With the subaerial debris flows calculating, this equat ion is good at calculating the velocity of non-hydroplaning subaqueous debris flows.