Abstract：The abutments of Yujianhe Arch Dam have hidden trouble to their safety because there exist many faults，joints and weak seams in the rock mass. Based on in-situ investigation and testing，it could firstly be decided that the block above the elevation of 1 034 m in the right abutment was the most dangerous one. Then，the 3D limit equilibrium method (LEM) and the 3D finite element method (FEM) were both used to calculate the stability coefficient of the block. The results got from the two methods were different，the first was 2.0，and the second was 3.0. To get the true result，the two methods were compared in physical model and mechanical model，and it was then found that the result of FEM was on the high side because of the yield criteria，and the result of LEM was on the low side because the load of dam was magnified in this method. By analyzing systematically，the final stability coefficient 2.4 was given out，which couldn¢t meet the requirement of the criteria，so it was suggested that the block should be treated.
