The layer number is one of the important structure parameters in laminate material. For laminate 7475/2091, the laminate with same thickness but different layer number from 2 to 20 were processed and studied. Experiment results show that the layer number of the laminate has a strong influence on the superplasticity of the laminate. Microscopy observations indicate that a metallurgical bonding at interface is obtained between two components in the laminates. There is a diffusion effect region on each side of a bonding interface. Cavities nucleate and grow there, especially at bonding interfaces in optimum superplastic deformation condition. The cavity evolution during superplastic deformation is an important factor that affects total elongation rate of the laminate.