K2＋010～+310 section of the diversion tunnel of Pianqiao Hydropower Station is located in heavily jointed rock mass. The surrounding rock mass has been greatly loosened and rockfall occurred due to delayed support after the excavation. In order to assure the tunnel stability and considering the tight construction period, the tunnel support is optimized and the worldwideused discrete element code UDEC is applied to simulate the complete tunnel construction and operation process so as to examine the stress and deformation distribution in rock mass at various stages of tunneling and to assess the optimized design of the tunnel support. Meanwhile, the simulation technology of tunneling and operation using UDEC is thus investigated.