By means of the routine observations, surface AWS data, NCEP/FNL Operational Global Analysis data, Doppler weather radar data, wind profiler radar data and GPSPWV data, we conduct an analysis of the extraordinary rainstorm in Jiangsu on 11 July 2016 The results indicate: (1) The residual low of Typhoon Nepartak, upper cold vortex and subtropical high were the advantageous synoptic background of this extraordinary rainstorm. The large cyclonic curvature at the top of the inverted trough and the pressure reduction of high trough caused a mesoαscale low in South Jiangsu, merging with the residual low enhanced the pressure gradient, which resulted in the increase of kinetic energy, leading to the formation of a southwest low level jet (LLJ), which is beneficial to the formation of the rainstorm. Three mesoβscale vortexes (D1, D2 and D3) are formed successively in the mesoαscale low, and the extraordinary rainstorm in Nantong developed with D3, with the center located around Nantong University, with the biggest rain intensity being 1512 mm〖DK〗·h-1. (2) The convective storm was triggered by the mesoαscale low in Nantong, and the precipitation latent heat release enhanced the upward motion, which benefited the formation and development of the mesoscale easterly low level jet and mesoβscale vortex D3 located in left. Meanwhile the middlelevel colddry air intrusion enhanced convective instability and vertical wind shear, multiplied the low centerofmass mesoγscale vortexes, continued to develop, and moved slowly, and then heavy precipitation continued and increased abruptly. (3) The sudden enhancement of the vertical wind shear appeared before the peak time of the rainstorm for 30 minutes early, and lowlevel velocity convergence (divergence) were obvious ahead of development (weakening) of the convective storm. The conclusions can provide valuable reference to nowcasting.