Abstract: 90°-phase conversion technique can make the main seismic event coincide with the geologically defined sandstone bed through rotating seismic phase for ninety-degree, and the seismic phases have lithological stratigraphic significance. This technology has the advantages of fast calculation speed and fully respecting the raw seivsmic data, it is not constrained by well data and the model, so it's especially suitable for offshore reservoir research target which has no well or few wells. Ninety-degree phase conversion technique achieved a good application effects on reservoir prediction of Neogene oil fields in Huanghekou Sag. It improved reservoir prediction accuracy especially made the thin bed interpretation much easier. This technology can be promoted to oilfields with similar geological conditions.