Composite materials show different mechanical properties in different directions which leads to complications in the prediction of their behavior. In addition to being inhomogeneous, behavior of composite materials is highly dependent on the curing process and many studies have tried to address these issues. Residual stress can induce high errors in prediction of composite material properties and leads to a difference between theoretical and experimental results. It has been observed that the humidity of environment and the chemical properties of composite materials are also important. Fewer studies have addressed thick layer composites and no damage theory has been developed for these materials. In this paper residual stress in thick layer composites have been studied. Using numerical analysis, the curing process has been modeled and mechanical properties of a thick layer composite are obtained and the induced residual stress in these composites has been assessed. Unlike thin layer composites, the stress in each layer is not specific and a tensile and compressive stress field can exist simultaneously in thick layer composites.