Using the travelling wave transformation instead of the more general function tr ansformation, the modified Jacobi elliptic function expansion method is improved . Some new periodic solutions of nolinear Klein-Gordon equation are obtained usi ng this method. When modulus m→1 or m→0, these periodic solutions dege nerate to the corresponding solitary wave solutions, trigonometric function solu tions or irregular travelling wave solutions. For some nonlinear equations, the general transformation would degenerate to the travelling wave reduction under certain conditions.