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Structures of Bi2Sr2CaCu2Oy single crystals, as grown, annealed in O2 and Ar at 400°C for 48 h, respectively, have been examined by X-ray diffraction. It is found that the crystal after annealing in O2 structurally has good quality, while after annealing in Ar it has bad quality. Most important, multi-layer structure is found from the high resolution rocking curve of the crystal annealed in Ar. Considering the change of the Tc value of the crystals after annealing in different atmospheres, we suggest besides oxygen content, structural modification may play an important role in the superconductivity of Bi2Sr2CaCu2Oy.