Abstract: Velocity model plays an important role in exploring tectonic evolution, deep structure, sedimentary basin analysis and energy resources exploration of a region offshore. According to our experience in the South China Sea, accurate stacking velocity is possible to be obtained from 2D multichannel seismic data and root-mean-square velocity converted to interval velocity then. Upon it a macroscopic 3D-dimensional velocity model of the study area may be constructed by the minimum curvature interpolation algorithm. Good results have been achieved. So far, we have preliminarily established the method of macroscopic 3D velocity modeling based on 2D seismic data and laid a solid foundation for future study of macroscopic 3D velocity modeling in the whole area of the South China Sea.