Abstract:The parameter values of rock mass have a direct bearing on its confining pressure. The parameter values applied in the design of a project should reflect the situation of the project in working stress state. The formula of confining pressure expressed in initial in-situ stress of in-situ test samples and the formula of surrounding rock pressure confining pressure in working stress state are established based on the example of deducing the deformation moduli of foundation rock mass of the high arch dam of the Hydropower Station No.2 on the Yellow River in working state from in-situ test results. The relationship between in-situ test results and confining pressure is established. The calculation results of the example are reasonable,which proves that the proposed method can be used in design.