Abstract: Drainage pipe network is a key element in urban storm water routing, but it is often simplified in modeling because of data availability and modeling capability. To identify the function of such networks and understand the influence of its complexity on hydrological responses, we develop a routing-enhanced detailed urban stormwater model (REDUS) and apply it to simulations of the Tsinghua campus drainage, focusing on comparative analysis of typical storm water processes in two systems: a single drainage system and a dual drainage system. Results show that in either system, the network contributes to a rapid and directional discharge of flood water, and that a lower complexity in modeling dramatically underestimates the flood peak and volume when smaller pipelines are excluded from the system. Compared to the cases with no simplification, a drainage system only including the truck pipelines underestimates the flood peak and volume both by 27% for the single system, and it underestimates by 37% - 56% and 18% - 32% respectively for the dual system. Although the dual system ensures more accurate and reliable results, it relies on more detailed data of the pipe network. This study provides a useful tool and helpful suggestions on how to model drainage pipe networks for sponge city construction.