Abstract: Block theory is an effective method on stability analysis of fractured rigid rock mass. There are a lot of discontinuous planes developed in rock mass of Jinping II hydropower station conveyor tunnel. So the stability of conveyor tunnel is related with the presence of unstable blocks on excavation planes. This paper deals with the stability of the conveyor tunnel with Block theory based stereo-analytical method on the basis of detailed investigation of rock mass data. It makes judgments on the movable blocks such as sliding types that are induced by all rock discontinuous planes on each excavation plane of the conveyor tunnel. A conclusion is obtained that the sliding type of blocks is mainly single sliding. A relatively few sliding types of double-sided sliding and vertical block falling are also found. Also, the obvious statistical distribution result on the movable blocks in the conveyor tunnel indicates that there are some more instability blocks in the left wall, the left and right arches than the right wall.