In this work the fracture process of steel honeycomb sandwich beams has been investigate by situ acoustic emission(AE) technique. Pre-cracks were made both for L-direction and W-direction specimens subjected to out-plane three-points bending loads. Damage initiation sites were observed in the vicinity of the crack tip. A series of curves among the AE counts, AE hits, AE amplitude, AE energy and loading time were obtained. Damage characteristics were discussed based on the above parameters. The results indicate AE characteristic parameters can reflect the damage and failure process of specimens. A good agreement was found between the experimental and analytical results.