The torrential rain on July 20, 2021 in Zhengzhou was one of the heaviest disasters in history. By using the observation and re-analysis data, the characteristics and main causes of the torrential rain are analyzed via statistical methods, such as the composite analysis and anomaly analysis. The results show that this torrential rain event was characterized by the extremely strong sudden, short-time and heavy rainfall, and prominent extreme.For the atmospheric pressure of 200.hPa, there are abnormally strong and stable high-altitude troughs and high-altitude cold vortices, which make the upper layers above the rainstorm area have a strong divergence condition. Moreover, the western Pacific subtropical high was significantly strong and shifted northward. Under the joint effect of the Typhoon “In-Fa” and “Cempaka”, the moisture transport and its convergence were extremely strong over Zhengzhou. The echoes over Zhengzhou are developing vigorously, and convective echoes are continuously converging, showing an obvious “train effect”. Additionally, the topography of the Fu-niu Mountain and the Tai-hang Mountain also contributed to the low-level convergence and ascending motion over Zhengzhou, and played an important role in the increase of precipitation. Therefore, the general circulation and extremely strong water vapor conditions in high, medium and low airs as well as the amplification of local topography were all beneficial to the development of the heavy rain, leading to the occurrence of extreme flood-causing torrential rain event in Zhengzhou on July 20, 2021.