Delamination in real composite structures, which generally tends to grow in two-dimensions, sometimes cannot be appropriately represented by the widely accepted test methods where one-dimensional (1D) beam specimens are typically employed. In order to compare and contrast the two-dimensional (2D) and 1D delamination behavior under Mode-II fracture condition, a numerical investigation was carried out in this work based on previous 2D experiments (Fig. 1) and end-loaded split (ELS) experiments. Three-dimensional finite element models (Fig. 2) were established for the simulation of the experiments, and a new cohesive zone model was developed to take into account the effects of a large-scale fracture process zone (FPZ) in the presence of resin plastic deformation, microcracking and fiber (bundle) bridging. The total strain energy release rate (SERR) for Mode-II delamination in 2D plates were found to be similar to that in 1D beams of the same bulk materials, whereas the cohesive relationship was significantly different. Membrane forces that originated in the 2D plates due to large deformation resulted in reduced mean shear tractions over the microcracking zone, which might lead to significant discrepancies in the fracture behavior compared to that in standardized beam specimens.