In order to design an economic and safe aluminum alloy cavity composite member to reach reinforcement requirement, the bending performance of aluminum alloy cavity composite member is studied considering the actual working conditions of aluminum alloy cavity composite members in the reinforcement process, and it is verified by numerical model. Firstly, the loading and failing process of specimens are described. And then the failure mechanism of specimens in various types is analyzed and the growth trend of bearing capacity, ductility and bending stiffness of specimens are obtained. The results show that: (1) The mortar crushing or aluminum alloy breaking is the sign that the aluminum alloy cavity composite member loses its bearing capacity. (2) The mortar material can significantly improve the bearing capacity of the specimens and reduce the ductility, but contributes little to the bending stiffness of the specimens. (3) The carbon fiber material can significantly improve the bending stiffness of the specimens and increase the ductility and bearing capacity of limitedly.