Abstract：The method combining the genetic algorithm with finite element method is applied to the first-stage back analysis of initial geostress field，for the large-scale area of Pubugou underground chamber area. And then，composite element method is adopted in the second-stage analysis of geostress field，for the local model of Pubugou underground chamber area，with considering important faults，and the range of the local model is the same as that of the model of stabilization analysis for underground chamber area. The calculation is based on the displacement boundary conditions. After the comparative analysis，it is shown that the two-stage analysis of geostress field，with considering important faults，not only provides exact initial stress of the faults，but also improves the initial geostress field，with small relative error. Additionally，under the advanced calculation level，in the first-stage back analysis of initial geostress field，the important discontinuity segments such as faults should be taken into account as more as possible.
