The middle atmosphere is characterized by the prevalence of atmospheric waves. The waves predominate the major variability in the area. The waves also play the role of controlling the various key aspects of the middle atmosphere through wave damping in the propagation of waves, e.g., exerting mechanical drag on mean flow and causing turbulent diffusion on constituent, in particular in shaping the structures of the general circulations. A brief retrospect in the development in these researches is provided at first. Meanwhile, the temperatures collected by a satellite mission (SABER/TIMED) are used to investigate the property of travelling planetary waves (PWs) in the stratospheric portion (20~70 km). In terms of the standard deviation of temperature, the variability of the wave family is observed, and the annual variation and latitude-height distribution of the variability are presented. The travelling waves are found to be prominent both in the low latitudes as well as in the extra-tropical area. As to extra-tropical area, by comparing to the concurrent variability of stationary PWs retrieved by using the same dataset, both the travelling and the stationary waves exhibit clear annual cycle attaining maximal variability in the late-winter and early-spring (LWES), with T-SDEV of 12~14 K. Moreover, during the summer time when the stationary PWs are strongly depressed, travelling PWs are instead to be the predominant perturbations of planetary scale. Estimation results in terms of T-SDEV show that during the yearly course, the travelling PWs are steadily the predominant waves. Among all the features of the waves, the vertical variation of T-SDEV suggests that the waves are subject to be saturated. For example, the T-SDEV increases with height from 20 km to 30 km, but from 30 km to the bottom of the mesosphere, the feature is replaced by a phenomenon that the T-SDEV exhibits independence of height.