The underground cavities of the Guandi Hydropower Station comprise four pressure division tunnels, a generator chamber, a main transformer chamber, a tail water control chamber and two tail water tunnels and arrange in the basalt mountain on the right bank of the dam. Based on the brief introduction of cavity arrangement, geological conditions, monitoring design and execution, the deformation magnitude and deformation characteristics of the three major cavities are focused on analyzing. The stability of the cavities is evaluated. The quality of the surrounding rock masses of the underground cavities of the Guandi Hydropower Station is good and the deformation is normally less than 30mm. However, some parts have large deformation due to the influence of the structure surfaces and the maximum deformation is 61.49 mm. Most of the parts with larger deformation are the middle and upper positions of the side walls and rock anchor beam positions. The structure surfaces have noticeable action for controlling the surrounding rock mass deformation. The stability of the cavities is good.