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Based on the conventional observation data, intensive automatic weather station observations, DopplerRadar data, the global final (FNL) analysis, etc., the spatial temporal characteristics, mechanisms and extremes of the extremely intensive precipitation from 15 to 18 July 2018 over the Beijing area are analyzed. The results show that there were three distinct precipitation “wave peaks” in this process. It was a typical warmarea rainfall in North China with the characteristics of long duration, great rainfall and wide coverage. (1) The extreme precipitation had a typical rainstorm circulation situation in North China: with highlevel divergence, around the edge of the subtropical high in the middlelevel, the slowly eastward moving front end of a trough, the lowlevel shear convergence of jet streams, and high temperature and humidity conditions. (2) There were abnormal circulation and physical conditions during the rainstorm process: the abnormally northerly subtropical high, the abnormally strong lowlevel southerly wind, and the extreme energy and water vapor conditions at the upstream of the rainstorm area and abnormally northerly ITCZ (InterTropical Convergence Zone). (3) There was a certain convective potential in this area, which was combined with the intense temperature and humidity transport of the southwest airflow at the middle and lower levels, and its forced uplift in the front of the mountains, and generated a convergence line with the night mountain wind to trigger the convection. The “train effect” and backward propagation of radar echoes were obvious in this process, and the echoes had the characteristics of tropical precipitation echoes with a low centroid.