Abstract:3D numerical simulation of typical sidewall and crown blocks is carried out for underground powerhouse of the Three Gorges Project. The following results can be drawn. (1) The sidewall block is in unloading stress state in vertical direction(y-direction) and horizontally perpendicular to powerhouse axis(x-direction),especially the latter and its main deformation is horizontally unloading rebound to excavated zone. (2) The compressive stress of the crown block is gradually increased in x-direction along with excavation,but the vertical stress is in unloading state in initial excavation stages and gradually increases along with latter excavation. Its main deformation is compressive in x-direction,but in y-direction,the lower part of block goes down because of unloading and the upper part goes up because of x-direction extrusion. (3) The stress-deformation field of blocks in process of excavation is beneficial to the stability of crown blocks,but unfavorable to the sidewall blocks. So,the calculation result based on rigid body limit equilibrium theory is over-estimated to sidewall blocks,but conservative to crown blocks. (4) The authors present that the method of qualitatively judging block general stability by its deformation and of quantificationally evaluating local stability by plastic zone characteristics.