Abstract: We propose an auto-calculation method for the catchment area of any given nodes in the municipal drainage pipe network.Firstly,the drainage pipe network graph is to be translated into directed graph.Secondly,the upstream nodes of any given node are to be obtained with the breadth-first search algorithm in graph theory.Thirdly,the calculation of the associated sides of the upstream nodes is carried out.Finally,according to the catchment area of upstream nodes and their associated sides,the catchment area of the given nodes can be calculated.And we put forward the correspondent programs for the new method.