The transient elastodynamic responses of the vacuum-filled and liquid-filled pipes surrounded by infinite liquid to external axisymmetric forces are simulated by employing the acoustic-structural coupled finite element method. The time-frequency distributions of the transients waveforms are obtained by the short-time Fourier transform （STFT）. Then the influence of the distribution of the external forces on the excitation of the guided waves is analyzed. The study shows that the L（O, 2） mode in the vacuum-filled pipe surrounded by the liquid is suitable for the pipe inspection because it is the fastest mode in a weakly dispersive and at- tenuative region of frequency. And it can be excited with high efficiency in the above region of frequency if the axisymmetric external force is applied on the inner or outer surface of the pipe axially. Analogously, the L（0,3） and L（0,4） modes in the liquid-filled pipe surrounded by the liquid are suitable for the pipe inspection.
