During early Ordovician time, a set of tidal flat dolostone deposited in evaporated platform slope in the northern side of Qingyang-Huangling Paleouplift, Ordos Basin. During the period of Caledonian orogeny, the paleouplift was uplifted accompanying with the rising basin while karst weathering -crust reservoirs with many types of anhydrite -dissolved dolostone formed within widespread different layers in the northern slope due to differential dissolution. Development and various types of karst reservoirs are dominantly attributed to these factors, i.e. the wide and gentle inclining slope, the low gradient of waterflow, the spreading crystal or nodular soluble anhydrite and salt grains. As the dense evaporite strata provide regional trapping condition for gas accumulation in weathering-leaching crust reservoirs in Fuxian Slope, it becomes an area favorable for gas exploration.