Abstract: In this paper, the mean monthly precipitation data series at 200 stations over the main land of China are subjected to harmonic analysis. It is shown that the annual march of precipitation over the main land of China is in general satisfactorily described by the first three harmonics, among which the first harmonie is the most important, The different regime of annual march of precipitation and the manner of transition from one regime to another are often clearly presented on the map of the first harmonic. The main features are as follows.1. The rainfall peak in the region south of the Yangtze river occurs in the latter half of May, and the normalized amplitude is relatively small, which shows that the precipitation distribution throughout the whole year in this region is relatively homogeneous.2. In North-China.North-East and some parts of Nortb-West and South. West China, rainfall peak occurs in the latter half of July or the beginning of August, and the normalized amplitude in most parts is equal to or greater than 1, which indicates that the dry season in these regions is relatively prominent.3. The transition between the afore-mentioned two regions appears quite clearly on the map. Not only the date of rainfall peak occurrence delays successively from the region south of the Yangtze river outwardly, but also the normalized amplitude increases outwardly.4. In East-China and the coastal area of South-China, the. rainfall peak occurs in the latter half of June or the beginning of July, and the magnitude of normalized amplitude in these regions is approximately the same as that in the region south of the Yangtze river.