Multi-objective Urban Green Space (UGS) design is essential for optimizing limited resources amid diverse urban development challenges. This study introduces a new design support tool that overcomes the data-intensive and expert-reliant limitations faced by urban designers. The tool integrates stormwater management analysis within the Rhinoceros + Grasshopper platform, offering three key features: (1) quantifying stormwater volume in the 3D model, (2) estimating the space required for stormwater management in UGS, and (3) providing options for stormwater management facilities for UGS design. Across the five scenarios, the tool effectively demonstrated (1) the identification that dispersed UGS layouts collect more stormwater than aggregated ones with the same total area; (2) the consideration of the impact of weather changes on passive stormwater collection; and (3) the provision of recommendations on facility areas and locations to enhance collaborative urban and landscape design, better addressing stormwater management needs. This design support tool empowers urban designers to create more sustainable and resilient urban landscapes by addressing stormwater management challenges effectively in UGS design.