Abstract: Unstable rock blocks are one of the geological natural hazard sources and can have a great influence on human life and engineering activities.The investigation of the unstable rock blocks,the evaluation of their stability and thier prevention measure are difficult tasks.The Nanmenwan unstable rocks have 20 blocks.The controlling design for the unstable rock blocks is very difficult for their complex geological characteristics.In this paper,in order to treat the unstable rock blocks,a stability evaluation criterion for unstable rock blocks at Nanmenwan is established on the basis of the study for the W6 unstable rock block with stereographic projection method.At the same time,the stability zone division at Nanmenwan is carried by the analysis of rock fractures development.At last,the control measures for unstable rock are also proposed for a guiding significance for the project.