The underground powerhouse of Houziyan Hydropower Station is located in the region with high mountains and valleys, and the regional geological conditions are complex. The underground powerhouse caverns have some typical characteristics such as high strata stress, large span, high sidewalls and large depth. The maximum principal stress is 36 MPa and the maximum vertical depth of the caverns is 660 m. During excavation, rock unloading has an influence on the stability of surrounding rock mass. In the paper, numerical simulation of excavation and support of the underground powerhouse caverns was performed by using the Fast Lagrangian Analysis of Continuum method (FLAC3D). Then the?distribution?characteristics of deformation field, stress field and plastic zones were analyzed. In addition, the numerical calculation results were compared with the results of scene monitoring and microseismic monitoring. It shows that the deformation of surround rock mass based on the numerical calculation coincides with the monitoring results. The regional aggregation of microseismic events happened in the region of stress concentrating. Given this, the deformation of the rock mass surrounding underground caverns can be predicted using numerical calculation. The results can provide guidance for the construction excavation and support.