Abstract: In this paper, the propagation characteristics of the taper pipe are studied by the circumferential guided Lamb wave. The wedge angle of the probe used to detect the reducer is selected by simulation software WAVE3000. And the propagation characteristics of the circumferential Lamb waves are analyzed for the different diameters. At the same time, the propagation characteristics of the circumferential Lamb waves with different excitation frequencies in the taper tube are studied, and the characteristics of the dispersion of the received signal and the signal-to-noise ratio are analyzed. The optimal number of excitation signals is given. The above studies provide guidance for circumferential guided wave detection of taper pipe.