Aluminum foam bar (AFB) with thin outer wall was prepared by melt foaming method. The effect of span, diameter and porosity on its bending deformation behavior was investigated by cantilever beam bending experiment and finite element simulation. Bending deformation behavior was recorded by high-speed camera and the relationship between load and displacement was obtained. X-ray micro-computer tomography (Micro-CT) technique based on 3D finite elements was selected to scan and to reconstruct AFB, by which numerical simulation was carried out. The results show that span has important effect on the failure behavior and the increased span leads to decreased energy absorption capacity. In addition, increased diameter and relative density contribute to peak load improvement. Finite element simulation results match well with the experimental results, which clarifies that cell walls fail due to different types of stress during the bending process. Crack propagation follows the weakest cell walls path link during the failure process.