Abstract: The geological conditions at the left dam abutment slope of Baihetan Hydropower Station are complex with wide spread faults and dislocation belts. Combining with hydrogeological data and field monitoring results, we analyzed the deformation law and corresponding control factors of the left bank abutment slope during the impoundment period. The results showed that: ① the maximum deformation occurred at the free side of the 800 m elevation downstream of the dam abutment, which was up to 17.2 mm. The slope deformation was mainly shallow deformation within 0~15 m, and the deep rock mass was less affected by impoundment. ② After impoundment, the shear deformation of the C₃ and C_3-1 interlayer staggered zones on the left bank and the LS₃₃₁₉ and LS₃₃₁ intralayer staggered zones occurred. ③ The deformation of the slope on the upstream side of the abutment groove was controlled by the reservoir water level, namely the underwater rock mass deformed towards the inside of the slope, and the rock mass above water creeped slowly towards the outside of the slope. The deformation of the downstream slope of the abutment groove is controlled by the weak structural planes, and the slope deformed to the outside and downstream side. Subjected to dam self-weight and arch end thrust force, the slope of abutment groove deformed towards inner mountain side. Compared with similar projects, the deformation at the left dam abutment slope of Baihetan Hydropower Station is at a low level during the impoundment period, and the overall stability is good.