Abstract One of the major challenges of oil industry is to predict the in-situ stress field accurately. Accordingly, different techniques have been developed to predict the reservoir stress field in the past decades. Inversion Technique is a powerful method which was developed to determine the minimum and maximum horizontal stress components and their direction using fracturing data, i.e., leak-off tests or mini-fracture tests, by solving an over-constrained system of equations. As compared to other indirect methods, the actual fracturing data is used in this technique to back calculate the stress field. In this paper, a new feature is added that enable us to determine the stress field using the data gathered during the production history of reservoir. In this approach, the effect of pore pressure changes on the reservoir stresses is incorporated into the Inversion Technique using constitutive equations of orthotropic rock model. Using the proposed technique, minimum and maximum horizontal stress components can be determined corresponding to different pore pressure during the reservoir life. According to the field data, the new formulation increases the prediction accuracy when fracturing data is gathered corresponding to different pore pressure. The proposed approach can be used for more accurate well design applications during the life of reservoir.