In order to explore the characteristics and causes of the abnormal autumn rainfall in the Yellow River Basin in 2021, we analyzed the extreme autumn rainfall of 2021 and investigated the circulation background and sea surface temperature (SST) anomaly characteristics of the years with extreme autumn rainfalls using daily precipitation data of 232 stations in the Yellow River Basin, monthly reanalysis data of NCEP/NCAR and monthly SST of the Hadley Center, United Kingdom Meteorological Office. The results show that the autumn rainfall in the Yellow River Basin in 2021 was abnormally more abundant than usual, deviating from the climatic state by nearly 8 standard deviations. Accumulated rainfall of 62.5% of the stations ranked among the top five in the same period of history, and 37.9% ranked first, showing significant extremities. This is because the short wave troughs that split from the bottom of the low trough of Balkhash Lake moved eastward and southward, and converged with the southwest airflow of the northwest side of the West Pacific Subtropical High (WPSH) in the south of the Yellow River Basin, resulting in abnormally more abundant autumn rainfall in 2021. Compared with the other years with extreme autumn rainfalls, the area, intensity and west ridge point of WPSH in 2021 were especially larger, stronger and more to the west, while the intensity of Indian Burma trough was weaker. The SST in the North Pacific in autumn of 2021 was 3.6 standard deviations higher than the climatic state and the abnormal degree ranked first among years with extreme autumn rainfalls. The abnormal SST caused the extreme autumn rainfall through the abnormal response of WPSH. This study can provide a reference for autumn rainfall prediction in the Yellow River Basin.