Abstract: Urban land use changes alter the runoff production and confluence relationships, thereby affecting the occurrence and development of urban flood disasters. This study focuses on the western district of Hangzhou, utilizing the Patch-generating Land Use Simulation (PLUS) model to predict future land use scenarios, and constructs the Storm Water Management Model (SWMM) to analyze changes in runoff production and confluence in the region. The results indicate that: (1) The PLUS model can predict future land use scenarios in the study area, with built-up land increasing by 248.43% and arable land decreasing by 54.59% by 2030 compared to 1980; (2) The SWMM model effectively simulates the runoff production and confluence process in the study area, with an error margin of less than 10%; (3) From 1980 to 2030, the overall impervious surface area in the region increased by 27.91%, with peak discharge under 50-year and 100-year return periods increasing by 281.4 and 301.5 m³/s, respectively, and total flood volume rising by 6,964,594 and 7,507,033 m³; (4) The peak discharge and total flood volume simulated by the SWMM model show a good linear relationship with the proportion of built-up land in the region. The findings provide deeper insights into the mechanisms by which urbanization influences runoff production and confluence processes, offering scientific support for urban flood disaster prevention and control.