Abstract: Through analyzing the size of rock-anchored crane beam, excavation structure of spiral case, electrical equipment layout of bus corridor and so on, the main cavern scale of Wudongde Hydropower Station is optimized. In addition, the relationship between the length of anchor rods and cavern scale at different parts of underground powerhouse is established by analyzing the data of 17 built domestic underground powerhouses. Combing with present specification, support schemes and parameters for different parts of the powerhouse are determined preliminarily. On this basis, a three dimensional numerical model is set up, and the stability of the surrounding rock for underground powerhouse cavern group under different conditions is analyzed. It can be shown that the layout of optimized underground powerhouse cavern group is extremely compact, and the powerhouse size decreases significantly. Compared with Baihetan Hydropower Station in the same period, the reduction percentage of ratio of plant span to spiral case size along the flow direction, and the ratio of plant length to spiral case size along the vertical flow direction is 10.6% and 15.7% respectively. Moreover, the deformation of surrounding rock can be controlled well by the determined rock support. Compared with other methods, the cable support method is advantageous to keeping cavern group stability and security, which has proved effectiveness and reasonability of the support design. Therefore，the results provide reference to construction safety of similar underground engineering.