Abstract: World-wide attention has been paid to the plunging point because it is the forming and persisting conditions of strat ified flows.Incipient plunging point Froude number (Fr) is the forming condition of stratified flows and the stable plunging point Fr is the persisting condition of stratified flows.A series of experiments were conducted in a flume to study plunging point of stratified flows of low density turbidity currents, high density turbidity currents and debris flows The rule of incipient plunging point Fr in uniform and straight channel was found.The incipient plunging point Fr of stratified flow is direct proportional to the head velocity of stratified flow at given width of channel and given concentration of sediment.Compared the different experimental results from others references, the results of this study have good reliability as they have good consistency.The results of this study are applicable only for the incipient plunging point instead of the stable plunging point and the transition between the incipient plunging point and the stable plunging point.But the stable plunging point Fr of stratified flows of high density turbidity currents and debris flows is very close to their incipient plunging point Fr.This approach is more desirable when the debris flow has strong viscosity.