The stress in a separator is mainly caused by the lithium diffusion induced deformation in the electrodes and thermal expansion differential between the battery components. To compute the lithium concentration distribution and temperature change during battery operation, multi-physics models have been developed previously. In this work, a macro-scale model for a pouch cell was developed and coupled with the multi-physics models. In this model, the porous battery components were treated as homogenized media and represented with the effective properties estimated using the rule of mixtures. The stress analysis showed that the maximum stress in the separator always emerged at the area around the inner corner of the separator where it wrapped around the edge of an anode and when the lithium-ion battery was fully charged. Numerical simulations were also conducted to investigate the influences of some design adjustable parameters, including the effective friction, electrode particle radii and thickness of the separator, on the stresses in the separator. The results provided the reference conditions for the improvement of separator materials and the design of lithium-ion batteries.