Thin-Ply CFRP (Carbon Fiber Reinforced Plastics) composite laminates with ply thickness as thin as 20 to 40 µm is effective in suppressing transverse cracks inside the plies of the laminate due to their fracture mechanics effects. In contrast, a large delamination tends to occur in Thin Ply CFRP laminates under impact loading. The authors’ research group has made collaboration with Prof. Fiedler and Dr. Kötter on the mechanical properties of Thin-Ply CFRP laminates, and we attempted to reduce the delamination in the laminates under impact loading by metal foil reinforcement and by Bouligand layup pattern. The residual strength as determined by CAI (compression after impact) strength was also dependent on the delamination and fiber breakage mode in a complicated manner. In this context, we have developed numerical models to deal with the damage in Thin-Ply CFRP laminates under imapct loading. As the first step, we employed a finite element approach using the DGD (deformation gradient decomposition) method, originally developed by NASA Langley research center. Regarding the damage characteristics specific in Thin-Ply CFRP laminates, numerical results were discussed in comparison with the experimental results. Some characteristic phenomena were effectively modelled for Thin-Ply laminates under impact loading.