Abstract: Flowing of oil-water two-phase flow in reducing pipe section is simulated with FLUENT software. Simulation results show that pressure and flow rate of fluid in reducing pipe section are obviously varied, and moreover, varied degree is subject to oil-phase content in the fluid. Through flowing simulation, flowing law for oil-water two-phase flow with different oil-phase content in sudden expansion pipe and sudden reducing pipes are discovered, which can be provide as an important reference for the operation of oil-water two-phase flow pipelines.