Abstract：In response to the limitation of conventional index for stability and optimal design of underground rockmass engineering with high geostress and the drawbacks of conventional energy release rate(ERR) rockburst index based on linear elastic theory without brittle failure phenomenon，local energy release rate(LERR)，a new rockburst index is proposed. LERR is obtained through tracing the variety of elastic energy density of each element and recording the maximal fluctuation when brittle failure happens during numerical calculation. With the new index，the intension of rockburst and the position and extent of failure zone can be predicted quantitatively during rockmass excavation under high geostress. Furthermore，total energy release of surrounding rockmass obtained by LERR can be used as optimal index for optimal design of excavation schemes. The results of example analysis of diversion tunnel of Taipingyi Hydropower station show that LERR is rational. Finally，LERR index is applied to optimal excavation scheme of the large underground powerhouses engineering of Laxiwa Hydropower Station at Yellow River.
