Abstract: Aiming at the complex calculation process and poor stability of vertical flow exchange in one-dimensional and two-dimensional coupled model for urban flood, an improved vertical flow exchange method is proposed based on the principle of node water balance. The nodes of one-dimensional model are divided into overloaded nodes and non-overloaded nodes. For overloaded nodes, the principle of node water balance is used to calculate the vertical exchange flow, and the vertical exchange flow calculation is integrated with the hydraulic calculation of one-dimensional model to realize simultaneously solving of node vertical exchange flow and pipe flow. For non-overloaded nodes, the variable head orifice outflow formula is used to calculate the vertical exchange flow, so that calculation of node backflow considering change of surface water depth is realized. Using the Infoworks ICM model as a comparison, simulation results of different cases are compared. Compare results show that the proposed method has a high degree of agreement with the simulation results of contrast model (Nash-Sutcliffe efficiency coefficients are larger than 0.8), and the proposed method has the ability to simulate vertical flow exchange process accurately and ensures water balance of the system. Therefore, the coupled model with improved vertical flow exchange method has significant application value for urban flood simulation.