The power house of Yantan extended hydropower project, with complex geological conditions such as fault f211 below the power house and quartzite on top of it, is a huge underground cavern with large span and high wall. In order to evaluate the stability of the power house surrounded by such complex geological structure, the numerical simulation excavation of power house with different location schemes were studied by the elasto-plastic 2D FEM method. The deformation and evolutive process of the stress with the progress of excavation were analyzed. On the condition ensuring the whole stability of surrounding rock mass, comparison optimization analyses were conducted on the power house location scheme. The rational location scheme was demonstrated. The final analyses results show that: (1) The mechanical properties of quartzite and its relative location to the power house has no obvious influence to the stability of surrounding rock mass.(2) The f211 is the main bad geological structure which affect the stability of power house. (3) The case of moving 10m upward of power house is the most rational scheme for the whole stability of power house. (4) The Supporting measures, which would has an obvious effect in controlling the influence on the stability of surrounding rock mass by weak geological structure, are suggested at the out-crop of f211.