Abstract: In this paper, using the method of multi-time scale, the large-scale motion in the tropics is studied.The characteristics of motion in three stages are obtained. The results show that the large-scale motion in the tropical atmosphere, similar to that in the middle and high latitudes, has two kinds of adjustment phenomenons, i. e. for the first stage, as the dispersion of the gravity wave is very quick there occurs the geostrophic adjustment, for the second stage,as the dispersion ot the longwave is slower there occurs the adjustment of potential vorticity.We suggest that the evolution process in the three stages of the tropical atmospheric large-scale motion can be regarded as the ovelam adjustment process of potential vorticity. It is a kind of non-linear process with the geostrophic adjustment process acting as its primary stage.