Vietnam has more than 3260km coast line and about one million square of EEZ. Now, Vietnam has project to survey and delinate 2500m isobath and slope of seabed for determine the out limit of continental shelf. With coverage for each track is 6 to 7 times compare to depth (in 2500m depth the coverage is 15.000,0 m to 17.500,0 m), with dm accuracy in positioning then the best method to use Multibeam Echo Sounder and DGPS Real Time. From collected data the authors can model seabed terrain in three dimensions.