In the present work, AZ91 Mg alloy /1060 pure Al explosive composite plates were annealed. The microstructures, elemental distributions and mechanical properties of the bonding interfaces before and after annealing were studied. The results show that, Mg atoms diffuse from AZ91 to 1060 during annealing process and the diffusion layer is in 1060 near the interface. The thickness of diffusion layer and the highest hardness of composite plates increase obviously after annealing. The layer of high hardness is in AZ31 near the interface in composite plates before annealing, however after annealing the layer of high hardness is in 1060 near the interface. Before annealing the hardness increases because of work hardening and after annealing the hardness increases because solid solution and intermetallic compounds form in diffusion layers. With the increase of annealing temperature, thickness of diffusion layers increase, recrystallization tendency is more obvious and deformation bands disappear gradually.