In recent years, there has been an increase in extreme precipitation, leading to significant impacts on residents" lives and causing urban flooding. Therefore, it is important to forecast extreme precipitation and analyze the precursor factors that lead to it. In this paper, we analyze the spatiotemporal characteristics of extreme precipitation that occurred in September-October 2021 in the northern region of China and reveal the circulation background and factors affecting extreme precipitation. The results show that the extreme precipitation accumulated over 220 mm, the strongest extreme precipitation event since 1961. The autumn precipitation in China is mainly affected by ENSO, with the developing La Ni?a forming an anomalous anticyclone that enhances water vapor transport. However, the influence of ENSO is mainly located south of 39°N, and the area north of 39°N is mainly associated with the anomalous activity of the MJO. The MJO was anomalously active in phase 3-5, which was 2-3 times the historical climatological state, and the anomalously increased intraseasonal-scale upward motion caused the water vapor convergence, which resulted in the formation of the extreme precipitation. Statistical analyses also show that the probability of extreme precipitation in the northern region will increase by more than 60% when the MJO is active in phase 4, which provides an effective idea for forecasting extreme precipitation in the north.