Abstract: Nylon 6 shows low impact strength values. By adding thermoplastic polyamide elastomers(TPAE), Nylon 6 alloy can obtain high impact strength values. PLM and SEM observations of the fracture surfaces and deformed regions beneath the fracture surfaces revealed that the fracture process of Nylon 6 was brittle, which was originated from the plastic constraint at the notch tip. The fracture of the alloy was also caused by the plastic constraint at the notch tip. However, the plastic deformation zone at the notch tip was composed of many voids and partially elongated fibrils, and this absorbed the impact energy. The plastic deformation was enhanced by the transition of the stress state from plane strain to plane stress. The final fracture occurred from the notch tip connecting voids in the plastic deformation zone.