Natural gas is rich in Ordovician Majiagou Formation in the center and east parts of Ordos Basin.Based on the study of sedimentary characteristics and the macroscopic control of tectonic evolution on reservoir development and gas accumulation,it is suggested that the good source-reservoir configuration relationship between the developing Majiagou cyclic reservoirs and the Upper Paleozoic coal measures as source rock is the cause of present multi-bedded gas-bearing reservoirs and wide gas accumulation in the weathering crust at the uppermost part of Ordovician strata.It is convinced that the Lower Paleozoic marine source rocks are of a certain hydrocarbon potential.It is emphasized that longitudinal or lateral migrations of Ordovician gas are important to hydrocarbon accumulation in the Middle and Lower Majiagou Assemblages,in which the potential structural-lithologic combined traps can be predicted to be prospective in recent.