This paper analyzes the extreme rainstorm that occurred in Henan Province in 17-22 July 2021 based on the observations from radiosonde, automatic weather stations, Doppler weather radars, and the ECMWF ERA5 reanalysis data. The results show that this process had the characteristics of persistence, extreme rainstorm intensity and obvious topographic precipitation. The extreme rainstorm happened under the stable large-scale synoptic situation. When the high pressure in the Sea of Japan extended westward, and typhoons In-fa and Cempaka moved northwestward, the southwesterly/westerly airflow which strengthened northward in the periphery of the Huanghuai vortex provided abundant water vapor and energy for the occurrence of the extreme rainstorm. The warm-wet advection forcing in the mid-low troposphere, strong convergence and uplift under terrain influence as well as weak north low-level cold air were the important conditions of the extreme rainstorm, and the transformation of the “strong-weak-strong-weak” convective unstable characteristics indicated that there were two complementary physical mechanisms during the extreme heavy precipitation. The morphological structure and evolution characteristics were different in various stages of extreme heavy precipitation convection system (hourly precipitation ≥ 50 mm). In vertical direction, convective systems (CSs) of the short-time heavy precipitation showed the characteristics of low-mass center (stronger than 55 dBz), stretching thickness of the echoes greater than 50 dBz over 5 km, duration over 90-120 minutes. Short-time heavy precipitation CSs developed backward clearly within about 30 km in front of Taihang Mountains. Continuous southward extension of the topographic convergence line formed by the westerly easterly/northeasterly wind around Taihang Mountains was one aspect, and on the other hand further development of the northerly wind before the mountain due to the cold pool effect of heavy precipitation works too.