Based on the hourly precipitation data of 119 national automatic stations in Henan and the atmospheric reanalysis data ERA-5, a detailed analysis of the precipitation characteristics, atmospheric circulation and environmental physical quantities was carried out. We also compared three extreme precipitation processes in Henan. The results show that: (1) The "21·7" extreme rainfall is significantly extreme in terms of maximum precipitation in one hour, three hours, six hours, one day, three days, and cumulative precipitation in the process. (2) In 200hpa, South Asian high and the low vortex near the East China Sea coexist steadily. In 500hpa, the subtropical high is stable and northward, and confronts with the continental high. This makes the atmospheric circulation stable and provides background for the occurrence of extreme rainfall in Henan. In 850 hpa, the superimposition of the easterly airflow on the south side of Pacific Subtropical High and on the north side of Typhoon created a deep water vapor channel from the Western Pacific to Henan, providing abundant water vapor. (3) During the "21·7" extreme rainfall period, the water vapor flux divergence was negative and the precipitable water in most region of Henan could reach 100mm, which means the water vapor was abundant. The large value areas of vorticity and vertical velocity appear near the eastern foot of Taihang Mountains, corresponding to the large value areas of precipitation. (4) Compared with two heavy rainfall processes ("75·8" and "12·8") in Henan, the similarity is that the typhoon was blocked by the Subtropical high when move northward and stopped. One possible reason why the "21·7" extreme precipitation is greater is due to the superposition of the warm anomalies of the Western Pacific Pool and the Indian Ocean, which makes the subtropical high is stronger and able to stably exist on the north side of the typhoon, thus resulting in record-breaking short-term precipitation during the "21·7" heavy rainfall.