Abstract: The severe deformation and cracking due to complex geological conditions in linings in the construction of this underground hydroelectric power plant has caused considerable concern. To monitor and investigate the stability of the surrounding rock and the behavior of reinforced concrete construction, field instrumentation has been set up and utilized, crack monitoring system was established. For the permanent stability of the underground caverns, further rock mechanics analysis and finite element analysis have been made. By synthesizing these findings, it has been shown tentatively that the "Earth Crust" stress is large and excavation induces stress redistribution in the surrounding rock. The stability of side walls has become stable by adopting some justifiable strengthening measures. Analysis shows also that the stress distribution is non-uniform, the excessive stress is increased not large and is localized in a relatively small zone in the rock pillar, and the shearing stress is not excessive. Therefore the rock pillar is still stable. Further investigations and field measurements are still under way.