Abstract: Based on the journal equations of elastic theory, this paper solved vibrational modes of axially symmetric ultrasonic solid horn with method of adjoint. Since the influence of cross-coupling is not ignored, the results from this paper are not limited in the cross sectional dimensions. For example, we have calculated the frequencies of three different sizes of the exponential horns with this method. The results of the calculation are much closer to the measurements than we get from the one-dimension method. The another advantage of adjoint method is usable to the calculation of non-exponential horn as Gauss or parabola stubs etc. The research works of application area of this method will be continued.