Stiffness of the rigid boundary is usually much more than the one of specimen in cylindrical axial compression experiment.But the stiffness of the real boundary is in keeping with the specimen.The difference of the stiffness between the real boundary and rigid boundary makes the experimental result disabled.This study discusses the difference of the two boundaries and reduces them.The difference of them has two sides.One is difference of material stiffness, and the other is the distribution of stiffness at the boundary of the specimen.In consideration of the cost of experiment, larger stiffness material is used in the optimization design.This means that the study is not evading the difference of the material stiffness and the distribution of stiffness is as the key in the optimization design.In order to describe the difference of the boundary, one suitable optimization object is needed in the design.