The abutments of Yujianhe Arch Dam have hidden double to their safety because there is a presence of many faults joints and weak seams in the rock mass. After establishing a three-dimensional model, we use Vector Algebra method to calculate the block stability coefficient before and after concrete presser foot handling. The results show that in normal condition, the stability coefficient raise from 2.45 to 2.70 after treatment; in checking condition, the stability coefficient raise from 2.09 to 2.30. But security reserves still remain low, so some monitor measures about right dam abutment may be introduced during later reservoir construction...