Problem in this paper is based on the Saint-Venant equations of the transfer function model.It was applied to urban drainage systems combined sewage overflow control to minimize spillover rate.Using the existing drainage system facilities，through flexible traffic control and optimization，the purpose of the smallest overflow ratio is achieved.Firstly，the general transfer function model used in drain pipes is derived based on Saint-Venant equations.Then，for the middle section of two flanking the node into the drains is further analysed，based on the above model calculation. Finally，MIKEURBAN software is applied to simulate，and a comparative analysis of the results between the model and the software is achieved.