Abstract: Flow pattern identification is significant in the research of gas-liquid two phase flow. Applied with OLGA, a transient multiphase flow simulation software used in the industrial design of the high-pressure large-diameter pipeline, numerical simulation on a gas-liquid two phase flow is performed, in which gas and water are used as transmission media. The inner diameter of the pipeline is 200 mm and the pressure is set as 2.0 MPa. The pipeline inclination ranges from － 70° to 90°. Based on the variety of the gas/liquid flowrate and the pipeline inclination, the gas/liquid flow pattern transition is studied. According to the 1 628 sets of simulation results, taking into account the fluid property and pipeline inclination, empirical correlations on flow pattern transition are established, which provides a reference to the flow pattern identification for high-pressure large-diameter gas/liquid flow pipelines.