When a foreign object crashes to a composite laminate structure, impact damages may be introduced in the laminates. The most common damage under low speed impact is a delamination. The delamination decreases the compressive strength of the laminate remarkably. The compression strength after impact (CAI) is considered as one of the most important mechanical characteristics in the advanced polymer composite materials. The CAI behavior can be understood as instability-related crack growth under in-plane compression. The post-buckling behavior of delamination-embedded laminate is very complicated because local and global buckling take place simultaneously. In the present paper welldesigned specimen was used in order to avoid the complicated post-buckling deformation. An embedded through-width delamination (ETWD) sandwich column specimen has been developed and applied to characterization of the post-buckled delamination. Theoretical analysis based on the elastic beam theory and finite element analysis have been carried out in order to investigate the post-buckled delamination. Deformation of ETWD sandwich column specimen has been analyzed and the energy release rate has been calculated. The crack tip stress field is in the mixed modes I and II. The effect of the mixed mode loading on the critical condition of delamination growth has been also examined and the critical stress has been calculated based on the linear elastic fracture mechaics. Onset of the local buckling in the delaminated laminate, the critical load of the delamination growth and propagation of delamination have been investigated experimentally. The analytical results have been compared with the experimental results, and a damage tolerance estimation method has been proposed by using mode I and II interlaminar fracture toughness of composite laminate.