A novel auxetic columnar honeycomb structure is introduced， in which four honeycomb structures of identical dimensions are designed by varying the number of unit cells. The effects of unit cell number on the mechanical behaviour and energy absorption performance of the honeycombs are investigated through impact experiments and finite element numerical simulations. The energy absorption performance is compared with the specific absorption energy of aluminum honeycombs of different masses. The results demonstrate that the honeycombs exhibit a unique compression-torsion coupling deformation mechanism during impact. The torsional motion of cell walls redistributes the internal forces， effectively absorbing and dissipating impact energy， thereby improving energy absorption efficiency. Further analysis reveals that the number of unit cells significantly affects the mechanical performance of the honeycombs， enhancing plateau stress and specific energy absorption， although compression displacement decreases. A comprehensive mechanical performance analysis indicates that HM4-8 demonstrates the optimal impact performance and energy absorption efficiency， making it suitable for high-efficiency energy absorption and impact protection applications. This study provides new insights into the optimized design of honeycomb structures， with significant engineering value， especially in fields requiring lightweight designs and high impact resistance.