Abstract：A new method is proposed which is used to approximately calculate the in-situ stresses with the logging data of casing deformation and to inverse the stress field of reservoir. Firstly，the uniform or average in-situ stresses may be determined on the bases of the damage pressure which can be determined by API. The relation among flexibility ratio, displacement ratio and stress ratio may be determined by analyzing of the elastic system with the casing and formation. The flexibility ratio depends on the elasticity and the geometry structure of the system. The displacement ratio is calculated by the logging data of the casing deformation. The stress ratio can be obtained by the flexibility ratio and the displacement ratio. Therefore，the nonuniform in-situ stresses can be obtained by the stress ratio and the average stresses. Secondly，taking the in-situ stresses as the foundational data，the finite element and inverse method are utilized to calculate the stress field of the reservoir. Finally，the method is applied to Daqing Oilfield preliminarily. The method makes it possible to inverse stress field in the formation where the data of in-situ stress measured are scarce.
