Abstract: Using conventional meteorological observations, satellite images, radar data and data from Automatic Weather Stations (AWSs) over Fujian, we have investigated the mesoscale system characteristics and the cause of an excessive rainstorm event triggered by super typhoon (1601) Nepartak including its circulation pattern in upper air, mesoscale system in ground level, satellite images feature and radar echo characteristics etc. The results indicate that mesoscale systems causing this event was strengthened due to the surface mesoscale convergence lines when the severe wind zone in periphery of the typhoon reached the coast of Fujian. The coupling of convergence in the low-level and divergence in the upper level and the unstable stratification formed by the dry air intrusion in middle troposphere provide a favorable environment condition for the occurrence of rainstorm. Taiwan' s terrain plays an important role in the following processes: the formation of hollow structure of the typhoon, the influence of strong peripheral winds, and the airflow in east side of typhoon splitting and converging together in the middle coastal areas of Fujian.