Observing by scanning electron microscope, the flat surface of calcined oyster shell began to change into fluffy one at 700℃. The pore density on surface increased obviously with the increasing calcination temperature but did not change anymore when the temperature was over 900℃. The X-ray diffractometer analysis showed that the powder of calcined oyster shell consisted of calcium carbonate in the calcite crystal structure. When calcination temperature increased to 800℃, the calcium carbonate changed into calcium oxide. The transformation ratio could be increased when nitrogen gas was added during the calcination. In comparison of the crystal structures of three kinds of calcined shell powder made from Corbicula fluminea, Meretrix lusoria and Crassostrea gigas, only the oyster shell powder appeared the calcite crystal structure before calcination. The other two shell powder transformated into calcite crystal structure when the calcination temperature reached 400℃. Furthermore, we found that the calcination temperature at 400℃ and 500℃ for Meretrix lusoria and Crassostrea gigas shells, respectively, could get the optimal study condition for biomaterials research which was determined by the indicators of their crystal structure, pH value and oxidation reduction potential.