Abstract: Many explanations were proposed for the deformation mode of the bank slope.The geological background of Three Gorges was introduced generally at first,and then the unique deformation phenomenon of the slope was serib.Through comprehensive study,it was pointed out that the unique deformation mode of the slope was controlled by the unique structure of the slope.The slope consisted of nearly horizontal layer,with soft layer and hard layer interbedded and perpendicular joints well developed.The strata outcropped in the slope were the second formation and the third formation of Badong group,which belong to middle Triassic system(T).The second formation of Badong group(T2b2) was purplish-red mudstone,which was vulnerable to weather and disintegration,and the third formation of Badong group was brittle and vulnerablion to dissolution.These characteristics of the strata led to deeply remoulding of the structure of the rock mass in the slope,and induced collapse of the structure of the rock mass.Thus,the slope took on some phenomena like slide or slump,and made the deformation mode of the slope complicated.