Abstract: Using conventional observation data，NCEP1 °×1°6h reanalysis data，diagnostic analysis on heavy torrential rain in the Northwest of Hubei which is caused by 1209 typhoon Saola inverted trough．The results show that:the process of strong precipitation weather effects on the typhoon Saola inverted trough，Southeast and East jet，the cold front from the North．Typhoon trough establishes a water vapor channel from the sea，which provides continuous vapor to the heavy rainfall area，and the rainfall intensity corresponds closely with the moisture flux divergence．