Abstarct: Due to the widespread and diverse applications of sheet mextals, recently, considerable studies have been focused on the formability of mextal sheets. Many of these researches, consider a plane stress model and neglect the effect of thickness stress. Additionally, study of thin sheet mextal behavior, demands considering microstructure parameters such as grain size and texture. Crystal plasticity finite element method (CPFEM) can be applied to such problems. In this dissertation, the effect of through-thickness pressure stress on the formability of aluminum alloy AA6022-T4 sheet is investigated baxsed on CPFEM analysis. A self-hardening behavior is considered for the strain hardening behavior of the slip systems. Further, for prediction of necking initiation and growth, maximum shear strain criterion is used for damage initiation and evolution. In order to implement the model in Abaqus finite element package, a VUMAT was developed baxsed on the discretized equations forward Euler integration scheme. After verification of the developed code, the parameters of the model were calibrated against the tensile test results. For simulating tensile test of 1 mm thick sheet, a representative volume of 3x1.5x0.5 mm^3،was partitioned into 14790 grains through a python code in Abaqus/CAE environment and then discretized using 50 μm tetrahedral linear elements. Using the experimental data available in literature and considering appropriate texture for the simulation domain, the crystal orientations were determined through Euler angles. Then, tensile tests were performed on the sample in the presence of the thickness pressure stress. The results show that application of the through thickness stress increases the strain corresponding to the necking initiation by 11.7% and thus postpones necking. A decrease of about 12.3% in tensile load in observed in this case. In biaxial tensile tests, the results show that the maximum shear strain is saturated at the initial stage of deformation and thus prevent evolution of damage variable and necking was not observed. Therefore, in this case, principal plastic strain damage model was employed. Results showed that application of the through thickness stress decreased tensile load about 18%, but the necking initiation did not change significantly.