Abstract: Based on conventional observation data, satellite images and NCEP/NCAR reanalysis data (1°×1°),the characteristics of a rainstorm caused by the Inverted Trough of Typhoon Mangkhut were analyzed. The major conclusions were as follow.After Landfalled Typhoon Mangkhut was decreased and moving to north-westward,the rainstorm occurred under the condition of the inverted trough.When the inverted trough was monving ,it affected by the terrain,the temperature-pressure field changed into baroclinic structure.The strong convergence in low layer led to the frontogenesis ,strengthened the frontal secondary circulation and the oblique upward flow along the frontal surface.The diagnosis of MPV showed that there existed the conditional symmetric instability (CSI) in the frontogenetical area,caused the mesoscale rainbands. There was a relationship between the frontogenesis and the moist symmetric instability ,they both happened in the same time and caused by the ,the area of CSI located in the east of the area of frontogenetical.In the vertical, the area of CSI located in the upper of the area of frontogenetical and the oblique upward flow.