Abstract: The migration and accumulation of oil-gas are closely related to the generation and evolution 0f the hydrodynamics,which controls the formation and distribution of oil-gas fields. Theoretica1 mode1s of the hydrodynamics for petroliferous sedimentary basins could be classified as two types, i.e; syrnmecal and asymmetrical models. With in a sedimentary basins, four different types of local hydrodynamic units can be recognized：① centrifugal flow caused by mudstone compaction at the depression area,② gravity—induced centripetal flow recharged by meteoric water at the basin edge generally,③ discharge area by cross-formational flow,or cross-formational flow-evaporation,as well as④ stagnation area. For the Ordos basin,the hydrodynamics in the Up-Palaeozoic reservoir is characterized by strong asymmetry,gravity-induced centripetal flow in the northern and eastern ascending areas of the basin,centrifugal flow caused by mudstone compaction in the western-southern declining areas of the basin,and cross-formational flow or cross-formational flow-evaporation in the areas between those areas mentioned above.By studying the migrating power,direction and channels of fluids,such as groundwater and nature gas,we can establish the present hydrodynamic model of the Ordos Basin.Groundwater flows from east to west,and nature gas migrates from west to east,which match with the distribution of fluid potential in the basin.Because of the inhomogeneity in the reservoir, distribution of the local hydrodynamic units follows certain patterns in the basin,which make the hydrodynamics complex.The exploration has also proved the formation and distribution of the hydrodynamics in the basin,because many gas fields have been found in the center of basin and groundwater is primarily located in the northern and eastern of Ordos Basin.