The anomaly characteristics of the weather and climate in China were outstanding in the summer of 2021. During this summer, many extreme weather and climate events tookplace with much more precipi- tation in North China. The intraseasonal variation of summer climate was significant. The pre-monsoonal rainfall season in South China started later, and the Meiyu in Yangtze-Huaihe River Valley and the North China rainy season started earlier than normal. The spatial distribution of monthly precipitation anomaly and its possible causes varied greatly in the summer of 2021. In June, the Northeast China cold vortex activity was very frequent, bringing more precipitation in North China and Northeast China. Severe floods occurred in Heilongjiang and Nenjiang River basins. The anomalous activity of the Northeast China cold vortex was mainly influenced by the positive phase of the North Atlantic triple from spring to June 2021. In July, the longitudinal rainy belt from the lower reaches of the Yangtze River to the eastern part of Inner Mongolia and the extremely severe rainfall in Henan were mainly affected by the long-term activity of the strong Typhoon In-Fa, the strong continental high and the Western Pacific subtropical high (WPSH). La Ni〖AKn~D〗a was an important external forcing factor for the above circulation anomalies. In August, the WPSH was much stronger and more southward. The associated anomalous low-level northwestern Pacific anticyclone resulted in anomalous convergence of moisture flux over the Yangtze River and “reoccurrence of Meiyu” weather. Further analysis indicates that the unusually active Madden-Julian Oscillation (MJO) in August was the critical cause for the significant turning of the tropical and subtropical circulations. MJO located in the Indian Ocean (Phase 2) lasted for 22 days with stronger average intensity, which was rare in history.