Abstract: Oil-Water two phase flow is common phenomenon in oil production with unique flow characteristic, which bring difficulties to the safe and/or economic design of mixed-transportation pipeline and determination of corrosion rate for two-phase transportation pipeline. The analysis on the oil/water two-phase flow phenomenon and laws is carried out by means of experiment and theoretical study of oil/water two-phase flow. This paper presents flow pattern and pressure drop model, programs the prediction software of flow pattern and pressure drop for oil/water two-phase flow. With this software, a calculation is made on the relative parameters of two oil/water mixed-transportation pipelines located at western Bohai Sea Oilfield and Suizhong 36-1 Oilfield. The result shows that the calculation results are fitted tightly against the actual operating conditions of pipelines.