Abstract:During the autumn of 2021 the climate of China featured higher temperature and more rainfall in general. The distribution of precipitation in China showed “more in the north and less in the south”. The autumn precipitation in West China is extremely heavy. The analysis of the causes of the unusually heavy precipitation in the northern region of China shows that from September to early October, the circulation in the middle and high latitudes of Europe and Asia was distributed in a pattern of “low in the west and high in the east”, the area between Baikal Lake and Balkhash Lake was under a significantly low trough, and the West Pacific subtropical high (WPSH) was stronger, stretching more westward and northward than normal, which was favorable for the intensive autumn rainfall in West China. Meanwhile, anticyclonic circulation anomaly over the western Sea of Japan was conducive to guiding the cold and wet airflow to the area between the Yellow River and the Yangtze River, and met with the warm and wet airflow from the Bay of Bengal and the South China Sea, forming an abnormal convergence area of water vapor flux and resulting in abnormal precipitation in the northern region. In addition, the abnormal more days with MJO is in the 3rd to 5th phases was also one of the favorable factors for precipitation in northern China. Further diagnosis shows that the SST in the tropical middle-east Pacific Ocean entered La Ni〖AKn~D〗a state again in autumn, and the SST condition of double-dip La Ni〖AKn~D〗a was favorable for the WPSH to be stronger and extend westward to the north. Therefore, the influence of the external forcing signal of SST combined with the circulation anomaly in the low and mid-high latitudes led to more precipitation in northern China during September to early October.