Abstract: An effective approach for formulating the initial geostress field was presented based on the ideas of sub-model method.Firstly,considering mainly the topographical influences of the nearby engineering projects,a large-scale monolithic model was created,and the geostress field was back analyzed initially with the neural network method.Then,considering influences of some main geological structures,the refined sub-model was created,and the more precise initial geostress field of the sub-model was obtained by finite element analysis iteration with interpolated displacement boundary conditions.Finally,the back analysis on the initial geostress filed of the left bank region for Xiluodu Hydropower Project was adopted to verify the described method.It was shown that the complication of problems was reduced by this approach and the more accurate initial geostress field could be obtained efficiently as a foundation for the engineering design and construction.