Abstract: Deep mining is gradually becoming more prevalent owing to the lack of shallow mineral resources. In the deep underground,the geological environment becomes complex,particularly has high in-situ stress. The CSIRO in-situ stress measurement method,as the international society for rock mechanics suggested as direct measurement method,is widely used all over the world. In shallow parsing type hollow inclusion strain gauge in-situ stress measurement of rock mass,the elastic modulus and Poisson’s ratio are obtained from the indoor biaxial loading data fitting of constant. In the deep rock mass showing the highly nonlinear,it is found that the relation between confining pressure and strain is nonlinear in the high pressure biaxial loading and unloading test,and the nonlinear relation is especially prominent as the confining pressure increases. The maximum confining pressure of the traditional biaxial loading test equipment is 20 MPa. It can not satisfy the high pressure biaxial test simulation of deep rock core release. Thus the traditional equipment is transformed to develop a set of high pressure biaxial loading test device. The theoretical maximum radial pressure is over 200 MPa,and the maximum confining pressure tested in the current test is 100 MPa. Based on the re- search and development of a set of high pressure biaxial loading test device,a high pressure biaxial loading-unloading test is carried out on the core of Sanshandao Gold Mine with a depth of 800 m. By analyzing the relationship between stress and strain,a non-linear hyperbola model between the mean stress vs volume modulus and shear modulus is pro- posed,the physical significance of the three fitting parameters in the model is defined,and the characteristic formula of the non-linear relationship between average stress and strain is derived. Based on the elastic mechanics theory,the maximum main in-situ stress without considering relieved strain path is 53. 11 MPa,its direction is 312°,and dip angle is 8° after the application of least square method to calculate. The optimization algorithm proposed in this paper takes the relieved strain path into consideration and divides the entire decommissioning process into multiple stages. The cal- culated parameters of elastic modulus and Poisson’s ratio at each stage are related to the stress state of the core,and conform to the deduced non-linear relation formula of stress and strain. The maximum principal stress of each stage su- perposition calculation of is 47. 78 MPa,its direction is 311°,and dip angle is 5°.