Abstract: It is found in this paper that the variations of runoff from the hydrometric station, Yichang, in the upper reaches of the Changjiang river in September and October reflect the variations of autumn rain in South-west China, Therefore, it is possible to utilize the data of runoff from the period 1882-1980 at Yichang to research into the fluctuation of autumn rain in Southwest China.The fluctuations of autumn rain in this region have cyclic character, the major cycle in September is about 3 year and 17 year, but it is about 13 year in October. The fluctuations of the autumn rain may be divided into many spells, some of them are above normal, but other are below normal. These spells are related with the condition of subtropical ridge in pacific in September and with Indian low in October.