Abstract: In Chencun Arch Dam ski-jump energy by opposite scouring at two sides is taken, downstream river basin experienced scouring equivalent that of a100-year return flood, two scouring dents are formed respectively at two sides. Analysis of scouring dents developing trend and geological condition contrast all indicated that the abnormal phenomena of depth of scouring dent at left side and location of the deepest point is caused by unfavourable influence owing to a large fault. At present the left dent that not endangered the stability of foundation rock of toe, but endanger the access road of left bank, should be treated duly.