Abstract: Due to the construction of Dan-Jiang-kou Dam and the reservoir regulation,the discharge downstream the dam has been approaching to a constant,and the sediment load has not been an independent variable any more.In this situation the effect of boundary condtitons upon the channel process is much bigger than that before the construction of the dam.Contrasting the soil mechanics properties of the bank and bed materials with the flow shear stress,the writer of this paper has established the follow-ing indices.1) the bank resistance index 2) the bedresistance index 3)the relative resistance index, In addition,we have proposed some other indices about boundary conditions and flow conditions.They are.4) the height from the bank top to the bed,H0;5) the lower floodplain restraint index, 6) the circulation in-tensity index, 7) the angle between the thalweg line and the bank,θ.In the above-mentioned indices,M is the percentage of content of silt-clay in river bank material,D the median grain diameter of bed material,m bank slope coefficient,H the average flow depth,B₀ the channel width at middischarge,B'₀ the channel width when lower floodplain is submerged,J the channel gradient,Q the water discharge,R the bend iradius and r the specificgravity of water.