Abstract: Modelling and evaluation of stormwater overflow and flood inundation characteristics is the basis for scientific assessment of flooding risks and formulation of drainage optimization measures. Taking eight plain polder areas in Dian Shanhu Town, Kunshan City as an example, this study applied topography, meteorology and rainwater pipe network data to analyzes the overflow characteristics of rainwater pipe network under extreme rainfall scenarios by using one-dimensional SWMM model, and quantitatively depicts the surface flood inundation area due to overflow runoff by two-dimensional CADDIES mode. Moreover, the the main influencing factors between rainfall events and flood inundation were explored, and two optimization strategies, i.e., enhancing the pumping station drainage capacity and increasing the water surface, were evaluated to identify flood regulation effect. The results show that: (1) the number of overflow points is affected by the surface properties and rainfall characteristics in the polder area. The extent of flood inundation area is significantly related to the rainfall characteristics. When the rainfall return period is greater than 0.63 a, the inundation area also increases significantly; (2) The flow volume of pipe network in Dian Shanhu town is overloaded under heavy rainfall, and the pipe network in the polder area cannot effectively deal with heavy rainfall events exceeding 50 a; (3) Increasing the drainage capacity of the pump station cannot reduce the number of overflow channels and overflow points of the rainwater pipe network, but can effectively reduce the submerged area; (4) Increasing the water area ratio can significantly improve the storage capacity of stormwater and floodwater. When the water area ratio of Xinxing polder, Yongsheng polder and Hongqi polder reaches 6.03%, 10.87% and 8.83%, they can effectively resist the river overflow caused by 100 a rainfall events. The results can support decision-making for flood disaster risk assessment and stormwater management in the study area and other plain polder areas.