The upper Paleozoic natural gas reservoirs in the Ordos basin are generally characterized by a large gas-bearingarea and low reserve abundance. On such a geological background, there still exist gas-enriched zones, with relatively highoutputs, high reserve abundance and stably distributed gas layers. The gas-enriched layers with relatively high permeability (thelower limit permeability is 0.5×10?3 μm2) are key factors for the enrichment and high output of natural gas. Based on coreobservation, analytic results of inclusions, and a great deal of drilling data, we proposed the following four mechanisms for theformation of high-quality reservoirs: (1) in the source area the parent rocks are mainly metamorphic rocks and granites, whichare favorable to keeping primary porosity; (2) under the condition of low A/S (accommodation/sediment supply) ratios,sandstone complex formed due to multistage fluvial stacking and filling are coarse in grain size with a high degree of sorting,low content of mud and good physical properties; (3) early-stage recharge of hydrocarbons restricted compaction andcementation, and thus are favorable to preservation of primary pores; (4) microfractures caused by the activity of basementfaults during the Yanshan Movement stage can not only improve the permeability of tight sandstones, but also afford verticalpathways for hydrocarbon gas migration. The upper Paleozoic natural gas reservoirs in the Ordos basin are generally characterized by a large gas-bearingarea and low reserve abundance. On such a geological background, there still exist gas-enriched zones, with relatively high outputputs, high reserve abundance and stably distributed gas layers The gas-enriched layers with relatively high permeability (the limiter permeability of 0.5 × 10 -3 μm 2) are key factors for the enrichment and high output of natural gas. Based on coreobservation, analytic results of inclusions, and a great deal of drilling data, we proposed the following four mechanisms for the formation of high-quality reservoirs: (1) in the source area the parent rocks are mainly metamorphic rocks and granites, whichare favorable to keeping primary porosity; (2) under the condition of low A / S (accommodation / sediment supply) ratios, sandstone complex formed due to multistage fluvial stacking and filling are coarse in grain size with a high degree of sorting, low content o f mud and good physical properties; (3) early-stage recharge of hydrocarbons restricted compaction and cementation, and thus are favorable to preservation of primary pores; (4) microfractures caused by the activity of basementfaults during the Yanshan Movement stage can not only improve the permeability of tight sandstones, but also afford verticalpathways for hydrocarbon gas migration.