Many material have different stress-strain relation in tension and compression, generally the relation is nonlinear. In this paper, we use two exponential functions to approximately represent the stress-strain relation of nonlinearly elastic material and analyze strength-difference structure of bars jointed to Rigid-body of fixed-point motion. The displacement method is used to derive the universal expression of calculating stress and strain. The nonlinear equations for computing angular displacement of the rigid-body has been given and general computing program has been worked out. They can be accurately and conveniently calculated. This problem has been solved satisfactorily.