Abstract: In order to study the influences on the phase velocities of different modes of the Lamb wave due to the variations of elastic coefficients caused by the material fatigue,the propagation characteristics of the Lamb wave are studied by simulations and experiments.It is found that the velocity shift of the high mode Lamb wave is more sensitive to the variations of elastic coefficients than that of the low mode.In a LY-12-CZ aluminum plate,the velocity shift of the A₃ mode is about 9 times larger than that of the A₀ mode.Then,high sensitivity can be obtained by using the high modes of the Lamb wave in the nondestructive examinations.