Based on the rainfall data of high-density sites, the extreme torrential rain process occurred in Beijing on July 20 2016was analyzed, and the spatial-temporal evolution process was clarified. The main conclusions are as follows: the total amount of therainfall in the storm center is above 350mm, roughly zonal distributed, located in the line of Fangshan district, Mentougou districtand Changping district, and also located in the piedmont plain with the altitude within the range of 200 -400m, indicating thetopographic uplift of transition from the plains to the mountain has significant role in the formation of heavy rain. The rainfalloccurred in the center of rainstorm has long-duration and high -intensity, and the peak of rain intensity lasts for more than 3hours, while the rainfall occurred in the sub-center of rainstorm being located in the districts of Huairou and Miyun has a shortdurationand high -intensity, and the peak of rain intensity lasts for less than 3 hours. The rain process is two -peak rainfallpattern, and the second stage is the main course of the rainfall process. In this stage, the total amount of rainfall reache up to184.7mm, with the approximately amount of “7·21” storm, reaching 20-year frequency standards, and the rainfall pattern has agood symmetry, following a normal distribution under the 0.95 confidence level. With the increase of the total rainfall, themaximum rainfall intensity of different sites shows linear increasing trend, and the occurrence moment of the maximum rainfallintensity advances (correlation coefficient is higher than 0.9); with increasing of statistical period, the increasing rate of maximumtotal rainfall gradually slows, which can be fitted by logarithm function (correlation coefficient is higher than 0.9).