Abstract: A regional rainstorm occurred in North China from August 12 to 13 2020. This process can be divided into two stages, warm-sector rainfall and frontal rainfall. In the warm-sector rainfall stage, there were three types of boundary layer conditions, including the low-vortex shear, topographic uplift, and sea-land low-level jet. To understand the mechanism of this warm-sector rainstorm in North China, the evolution characteristics, circulation background, and the three different boundary layer conditions in the warm-sector rainfall stage during this rainstorm were analyzed, using multi-source data including the meteorological observation data, the infrared cloud image of FY-4A satellite, doppler weather radar data, ERA5 reanalysis data, and wind profile radar data. The results are as follows. (1) This rainstorm occurred in the southerly warm and humid airflow along the periphery of the subtropical high. The warm-sector rainstorm was caused by mesoscale convective systems under three different kinds of boundary layer conditions. (2) Three mesoscale rainfall centers were identified, which were the spiral rain band in central and southern North China (region Ⅰ), the band-shaped rain band along the Taihang to Yanshan Mountains lying in the southwest-northeast direction (region Ⅱ), and the block-shaped rain band along the west coast of the Bohai Sea (region Ⅲ). (3) For region Ⅰ, the low-vortex shear system and wind convergence were the key causes triggering the heavy rainfall. The heavy rainfall was located on the right front of the moving direction of the vortex, causeing a 16-hours long-persisting and intense precipitation. For region Ⅱ, the topographic lifting and convergence motions were the major causes of the heavy rain band. The intense rainfall occurred in the piedmont plains and lower areas of the Tainhang Mountain and lasted 6 hours. For region Ⅲ, the boundary layer jet combined with the convergence effects of the sea breeze front were the major causes of the heavy rainfall. Heavy rainfall was observed in the convergence zone in front of the easterly jet, which lasted for a short duration, with the rainfall only lasting 4 hours.