Based on conventional observation data, regional automatic station data of Hunan Province, NCEP reanalysis data and Changde Doppler radar data, the mesoscale characteristic of extreme rainstorms occurring repeatedly in the north of Hunan Province from 8 to 15 August 2016 affected by several easterly waves was analyzed comprehensively. The effect of the Wuling mountains topography on rainfall increase was further verified by WRF-ARW mesoscale numerical experiments. The results are as follows: (1) After the typhoon 1604 landing at Shenzhen of Guangdong Province and moving northwestward and the typhoon 1605 moving northward, the western Pacific subtropical high rapidly extended westward and controled east China and coastal areas. At this time, the easterly wave disturbance at the bottom of the subtropical high provided the circulation background for extreme rainstorms. (2) The non-uniform heating near the ground provided sufficient thermal instability for the strong convection near the easterly wave trough, the surface mesoscale convergence line played an important role in triggering and strengthening the convection. (3) During the eastward movement of the boundary-layer warm moist air, a deep mesoscale vortex formed in east side of the Wuling mountains, which was the main reasons for the extreme rainstorm formation. (4) The topographic numerical sensitivity experiment further verified that the existence of the Wuling mountains was beneficial to the development and maintenance of strong convection on the east side of the mountain under the guidance of the easterly wind flow.