Abstract: Research progress in pressure drop theory of stratified flow pattern and dispersed flow pattern for oil-water two-phase are reviewed. For the former, two-fluid model, a more mature model in research, is introduced, and the key of which rests with the calculation of frictional drag coefficient between oil-water two-phase interface) for the latter, the key of which rests with thecalculation of oil-water two-phase mixed fluid viscosity. Problems in theory research of the oil-water two-phase pipe flow are analyzed and theory research direction is put forward to meet the urgent needs of actual pipeline operation.