Abstract: Taking the Wuchengxiyu region as an example, based on the long-term sequence daily rainfall and water level data, the cumulative anomaly method, Pearson frequency curve and Kriging interpolation method are used to analyze the changes of the water level and the storm flood return period. The change regularity and causes of the flood return period and the storm flood in the typical plain river network area under the background of urbanization are discussed. The analysis results show that the return periods of rainfall with different magnitude are ahead of schedule, and extreme rainfall is frequent and its frequency increases in Wuchengxiyu region. The occurrence frequency of the small-scale flood events (T=5, 10, 20 a) in the Wuchengxiyu region has increased, and the return period of the larger-scale flood peak stage (T=50 a) is obviously different between urban and suburban areas. The flood with 50 a return period in 1960 increased to 68 a in 2010 at Changzhou station affected by polders, with overall flood level reduction, while the flood with 50 a return period at Baishaoshan station in suburbs decreased to 32 a in 2010, with overall rise of flood level. The increase of the frequency in the small magnitude flood events was mainly caused by the rainfall increase, urban expansion and the attenuation of the river network and water system, and the flood peak water level in 2010 under the same magnitude of rainfall in 1960 continuously increased. The construction of the hydroprojects such as sluices, pumping stations and embankments has played an increasingly important role in regulating higher-level floods, resulting in a reduction of flood risk in the urban areas. For different magnitudes of the flood peak water level, the changes of the underlying surface characteristics and the influence degree of the hydraulic engineering construction are different. The analysis results can provide a technical reference for the study of the flood control safety in this area.