Abstract: There is along low-angle fauh extending in the dam foundation from BL51 to BL53 in Yunfeng dam，and it is unfavorable for stability against sliding. Various of calculated results show that if the lateral shear strength of rock is not considered, the coefficients of sliding resistance for BL51,BL52 would not meet the requirement of specification, whereas, if advantageous factors concerned such as lateral shear of rock are considered, it would meet requirements. Observational results during many years have shown that the deformation changes within normal confines, uplift pressure in the dam foundation is pretty lower, seepage in dam foundation is not obvious, the dam operates in normal condition. The lateral shear of rock has an impact on the stability against sliding for BL51, BL52 somewhat, but the impact has considerable uncertainties，additionally scourholes downstream is approaching the dam toe, no support for the end rock of BL51, BL52, thus, some reinforcement measure steps should be taken necessarily.