Abstract: Extracting urban features from dense building is essential to the simulation of urban flooding using classical twodimensional models.These urban complex structures are parts of boundaries in the simulation domain,where the mesh may be locally refined.As a result,the largescale urban flood simulation may not be feasible due to limited information in urban buildings.In this study,the classical twodimension shallow water equation is improved through the introduction of a plot ratio coefficient that can represent the building influence on urban flood simulation.The modified two dimension shallow water equation is solved by a finite volume method with artificial upstream flux vector splitting.The improved model is tested in two numerical case studies.The result shows that the model is able to simulate urban floods with an acceptable accuracy.At the same time,the requirement for urban feature extractions is significantly reduced.