Abstract: Based on the meteorological and hydrological data, statistical methods were used to analyze the abnormal characteristics and causes of rainfall in the autumn flood season in the upstream of Hanjiang River in 2021. The results show that the autumn rain in the upstream of Hanjiang River in 2021 has the characteristics of early onset, long duration, more rain days, large rainfall, and periodic heavy rainfall. The circulation characteristics are as follows: there is a stable jet stream center in North China at 200 hPa, and the upstream of Hanjiang River is in a upper air divergence area. At 500 hPa, the circulation pattern in middle and high latitudes of Eurasia is negative anomaly from Balkhash lake to Baikal Lake and Mongolia region, which is conducive to the southward movement of cold air from northwest. The subtropical high over the Western Pacific is abnormally strong and westward, and the ridge line is stable near 30°N, which is conducive to the longterm maintenance of the rain belt. In addition, there is a negative anomaly in autumn SST over the equatorial Middle Eastern Pacific with more autumn rains in the upstream of Hanjiang River, which is consistent with the La Nina typical SST anomalies in western China.