A heavy rainstorm occurred in autumn in Nan’an is analyzed by means of the regular observation， intensive observation from the automatic station， synoptic map， physical parameters， and cloud pictures to study the influencing weather systems and water vapor conditions of this heavy rainstorm. The atmospheric instability and its dynamic mechanisms are also studied.By analyzing the evolution of the weather systems in combination with the related physical parameters， it is found that the tropical depression and cold air are important factors for this heavy rainstorm， and the application of the sounding data plays an important part in quantitatively analyzing the evolution of the weather systems.