Abstract: To evaluate the stability of the surrounding rock of underground powerhouse in Three Gorges Water Conservancy Project, this paper applies block theory to screen out the main structural surfaces from the faults and fissures of the right bank main plant, identifies the four key blocks on the side wall, and analyzes the instability probability of the blocks by Monte Carlo method.The result shows that the destabilization probability of blocks 1, 2, 4 is close to or reaches 100% regardless of working conditions, and the destabilization probability of block 3 reaches 63.75% under seismic conditions, which indicates that the poor stability of the surrounding rock of the underground plant.In order to improve the stability of the underground plant, three engineering layout adjustment schemes were presented.Among them, option 1 can make two blocks disappear, the instability probability of blocks 3 and 4 is 0, and the volume of block 1 is greatly reduced, and the instability probability under seismic conditions drops to 34.02%.It enhances the stability of the surrounding rock of the underground powerhouse and regard as the preferred solution.