Abstract: There are few CFRDs built on thick alluvium deposits with dam height of more than 50 m.So do the relative design and construction experience.The 50.8 m-high Dahe CFRD built on 20～37 m-thick alluvium deposits is now in the preliminary design phase.Its right face slab 41.7 m in height is perpendicularly connected with the right bank of a mountain and the left toe slab 15.3 m in height is perpendicularly connected with the left bank of another mountain.Such topographic characteristics of mountain body and the relative design scheme are apparently different from those of other CFRDs built on thick alluvium deposits.Since the excessive deformation of perimetric joint would lead to failure of seal materials and cause water leakage,3D finite element stress-deformation analysis was carried out.3D finite element mesh with 19250 elements including surrounding mountain and thick alluvium deposits was established by use of advanced grid discreteness technique.Large scales of equations solving method were adopted in the procedure and the computer calculation time was greatly reduced from 40 hours to 20 minutes.Therefore the behavior of the dam and the joint of seepage prevention system was obtained in a short time,and the results would be helpful to the design of Dahe CFRD.