Abstract: According to the hydrodynamic model of two-phase flow in pipelines (Beggs-Brill) and combined with the theory of the network graph, the governing equations are formulated for hydrodynamic calculation of the oil-gas gathering network. The equations consist of the node continuity equation, loop energy equation and two-phase flow model equation. By the linear treatment, the governing equations are solved through iteration. The hydrodynamic calculation is the basis on the calculation of gathering pipeline network and optimization of network.