Abstract: The geological condition of a high and steep slope is comp lex. Itsweak structural p laneswell develop. The excavated height and ratio are high. The excavated faces are many for the sake of the space of the deformation. There are many failure evidences at the slope. On the basis of geological condition investigation, the rock mass structure and the affected factors of the slope are studied. It indicates that the deformation of the slope is controlled by weak structural p lanes in weathered and off - loaded rock mass. The deformation and failure mode is block failure by combination relations of structural p lanes. The future deformation characters are simulated with 3DEC. The monitored data shows that the stability of the superficial and the manipulative block is low. The whole slope could fail.