Abstract: With the development of water conservancy and hydropower engineering，many underground caverns with large span and high side wall have been excavated.The stability of their surrounding rock is the key problem in the design and construction process.Based on the underground house group layout in the expansion project of Yantan Hydro-power Station and the geological conditions of their surrounding rock，a FLAC^3D numerical analysis model is established.The process of the excavation is simulated，and the distribution character of the displacement field，stress field and plastic zone after the excavation and the distribution law of the stress concentration area and the potential damage zone of surrounding rock are studied.The analysis results indicate that fault intersection and cavern crossing are the main factors influencing the surrounding rock stability，while dikes that are not intersected with the caverns have little impact.Finally，the caverns stability is evaluated comprehensively and some useful conclusions are made.

Key words: Yantan Hydropower Station, Underground plant houses, Surrounding rock stability, FLAC^3D