Abstract: Finite element simulations are performed to study the effect of randomly removing cell wallson the dynamic crushing behaviour of honeycomb structures. The influences of the imperfection andimpact velocity on the deformation mode and plateau stress are investigated. Simulation results revealthat both imperfection and impact velocity affect the deformation modes as well as the criticalvelocities of mode transition. It is found that the plateau stress is proportional to the square of theimpact velocity when the imperfect honeycombs are deformed at transitional mode or dynamic mode.When the impact velocity is near the critical velocity between transitional mode and dynamic mode,honeycombs with small fraction of imperfection exhibit higher plateau stress, comparing to those ofregular honeycombs having the same relative density. However, when the imperfection furtherincreases, the plateau stress decreases obviously near the critical velocity between quasi-static modeand transitional mode.