Abstract: The Jacobi elliptic function expansion method can’t be applied to the “rank” different kind of nonlinear evolution equation was proved by introducing a concept of “rank”.Moreover,the tanh function and many kinds of the double function expansion method are suitable to solve not only the “rank” same kind but also the “rank” different kind of nonlinear evolution equation by extended the proof.

Key words: hyperbola function method, traveling wave solution, rank, nonlinear wave equation in elastic medium