Abstract: The mode conversion is one of the important characters in guided wave detection, so the determination of guided wave modes plays an important role in the detection. The in-plane and out-plane displacements at the outer face of aluminum pipe are got numerically when exciting the comb transducer using tone burst signal to generate axisymmetric longitudinal waves. The collected displacement signals are processed by time-domain method, two-dimensional fast Fourier transform and matrix-pencil method respectively, so to identify the guided wave mode in pipe. The processing result shows all the three methods can be used to identify the guided wave mode with their own characteristics and limitations, respectively.