The evolution of the organizations and the synoptic features of four successive mesoscale convective systems (MCSs) in the Beijing-Tianjin area under the background of the Northeast China cold vortex (NCCV) during 21 hours from 0400 UTC to 2400 UTC on July 22, 2009 was examined by using radar, surface observations, sounding data and ERA5 reanalysis data. The results showed that the convections in the four processes had different organizational patterns owing to the complex interaction among the shallow trough in the northwesterly flow in the middle troposphere to the southwest of the NCCV, the associated lower troposphere trough and cyclonic vortex, the southwesterly warm and moist flow, and cold pools under the background of long-lasting northwesterly flow to the southwest of the NCCV. The first process was triggered in north Hebei Province by the frontogenesis caused by a shallow trough on the west to the NCCV. A southwest-northeast oriented weak convective line was formed with the cell in north Beijing and developed the fastest and strongest. It evolved into a supercell and a bow echo later on. It produced cold pool which lifted the warm and humid air from the southwest producing series cells to a northwest-southeast oriented backbuilding pattern across the Beijing-Tianjin area. The second process was triggered by the cold pool of the first process on the south of Beijing and formed a supercell. The westward outflow of new convection of the first process made the supercell evolve into a southwest-northeast oriented backbuilding convective line. In the third process, a vortex in the lower troposphere formed corresponding to the strengthening of the trough to the south of the NCCV. The northerly wind on the west of the vortex in the lower troposphere converged with the southerly wind on the northwest side of the high-pressure ridge in the lower troposphere, producing multiple northwest-southeast oriented linear backbuilding convective lines. The echo training of these backbuilding convective lines caused heavy rainfall in Tianjin.. The fourth process started with two linear convections triggered respectively by the frontogenesis generated by another shallow mid-troposphere trough on the westsouth to the NCCV and the shear line generated by the NCCV in north Tianjin. The two linear convections merged into one due to the shear line in the lower troposphere with the southern part evolving into a bow echo. Some of the bow echoes had bow and arrow structure in the evolution of the four processes.