Abstract: With the development and exploitation of oilfields, the simultaneous flow of oil, water and gas become a common phenomenon in transportation pipelines, which would make the transporting process much more complicated. Due to the development of offshore oilfields, the transportation technology of oil-water-gas three-phase flow has been the spot at home and abroad since the 1980's. During the design of three-phase pipelines, the hydraulics calculation, especially the theory of pressure drop calculation, is major factor to be considered. This paper summarizes the research achievements of pressure drop calculation theory in three-phase flow, points out the problems and difficulties which are demanded further researching as well, with the purpose of guiding reference for further research in this field.