Abstract: Influenced by canyon topography, the CFRD built in canyon areas will cause the stress arching effect in the rivercrossing direction.The stress arching effect makes it difficult for the rockfill to be fully compacted at the bottom of the dam.Starting from the forming conditions, 3-D FEM is used to compare the distribution of the major and minor principal stresses of the CFRD with wide narrow valley, in order to reveal the formation mechanism of internal stress arching effect of CFRD in canyon regions.The distribution form and range of reasonable arch axis of stress arching effect at the bottom of CFRD are studied.The bottom rockfill at the center of the valley is most affected by the stress arching effect.The influence area accounts for about 23%of the overall height of the dam.The research results may provide a reference for reducing the adverse effect of stress arching effect of CFRD in canyon area.