Abstract: In order to better grasp the hydraulic situation of oilfield gathering and transportation pipeline network, a hydraulic calculation method based on object-oriented idea and binary tree was proposed for the gathering and transportation process with single-pipe annular watering which is common in oilfields. In this method, the oil & gas gathering and transportation pipeline network is represented as a combination of instanced objects, and the parameters of the object are stored in fields and attributes. Then, the hydraulic calculation model was established. Based on the binary tree theory, the flow, temperature and pressure of the oil gathering pipeline network and watering pipeline network of the system were solved in different ergodic orders. Accordingly, the hydraulic calculation software for oil & gas gathering and transportation pipeline network was developed, which can be used for the calculation of gathering and transportation system in actual production. It is indicated that this method can greatly reduce the workload of early modeling and has the advantages of high calculation speed, strong adaptability and good stability, and the final calculation error is about 5%, indicating its high value of practical application.