In the ultrasonic guided wave inspection of hollow cylinders, defect sensitivity of a wave mode is critical for improving results. In order to achieve a high sensitivity of defect detection, it is important to concentrate energy on the expected defect spot. A study of the particle motion contributes to determining the radial energy distribution (known as wave structure) in a pipe. In this paper, the normalized displacements of axisymmetric and non- axisymmetric longitudinal/torsional wave modes are simulated by using the normal mode expansion method. Our investigation shows that wave structures are highly frequency-dependent. Particularly, the dominant particle motion direction, of either a single wave mode or a mode family, changes with frequency variety. Hence, this particle motion study can also help the phased-array focusing inspection technique by determing the particle motion component and the relationship to focusing.