Abstract: The effects of concentrated defects on the in-plane dynamic crushing of triangular and quadratic honeycombs are numerically investigated by means of the explicit dynamic finite element simulation using ANSYS/LS-DYNA. Research results show that for concentrated defects, the concentration position of the defects, as well as the defect ratio, is an important factor that should be considered in the material design. Along with the increase of the defect ratio, the plateau stress and the absorbed energy are all decreased, the increase of the impact velocity weakens the effects of defects. The defect concentration position has great influence on the dynamic response of honeycombs, and triangular honeycomb displays greater sensitivity. These results will provide helpful guidance for the dynamic optimum design of the honeycombs.