Based on the real-time observed data and ERA-Interim 1°×1° 6h reanalysis data, the flood-resulting rainstorm overHunan Province in June 2017 were diagnostically analyzed. The results show that the upper cold vortex and subtropical high wereremain steady, which formed a favorable large scale environment for the rainstorm occurring, and the low vortex shear line andground occluded front were the major influencing systems. The enhancement and proximity of 2 high level jet induced the eruptionof the low level jet. Because of the enhancement of the coupling of high and low level jet, the rainstorm was strengthened andsustained. The low level jet provided abundant water vapor and unstable energy for the occurrence of the rainstorm. The rainstormarea showed significant convective instability, and the intensity of rainstorm increased with the increase of vertical gradient ofpseudo equivalent temperature. The large area of water vapor flux and convergence provided references for forecasting the fallingarea of rainstorm.