Rainfall is one of the leading causes of urban flood inundation, and different rainfall characteristics have different influences on the urban flood inundation risk. In order to investigate the influences, an urban flood inundation model of a southern city in China was established to systematically analyze the influence of design rainfall pattern and duration characteristics on urban flood simulation results with the application of the integrated catchment model (InfoWorks ICM). To evaluate flood inundation risk in the study area, 3 rainfall patterns and 3 rainfall duration under 4 return periods were chosen for the combinations of a total of 36 different design rainfall scenarios. By comparing the results of the scenarios in terms of inundation depth, inundation area and inundation volume, it was found that under the same rainfall pattern and return period, the influence of rainfall duration on inundation depth varies within a certain range; in all scenarios of different rainfall patterns and duration, the locations of the inundation sites basically remain the same; the inundation area is affected by both rainfall patterns and duration, peak inundation volume is influenced more by rainfall patterns than by rainfall duration, but total inundation volume is influenced more by rainfall duration and less by rainfall patterns. This study quantified the influence of different design rainfall characteristics on the urban flood inundation simulation results which aims to provide a technical basis for urban flood inundation early warning and emergency management.