In order to study the influence of the structure of core sheet, the ratio of the diffusion bonding area between the core layer and cover layer, and the ratio of diffusion bonding area between core sheets on the strength of multi-layer structure fabricated by superplastic forming/diffusion bonding process, FEM is used to analyze the rigidity and strength of different parts with different structures of core sheet and process parameters. In the research emphasis is put on two critical factors:0.5H/L and the elongation. The results show that the structure of core has greater influence on the rigidity and strength of multi-layer titanium hollow panel structure and the controlling of the value of 0.5H/L and elongation can realize maximal rigidity and strength, which maximize the overall advantages of multi-layer structure. Meanwhile, the radius of corner between the two near core sheets have greater influence on the ratio of diffusion bonding area between core sheet and cover sheet and two near core sheets, thereby affecting the strength and rigidity of multi-layer structure.