Abstract: In order to investigate the development features and control factors of the Ordovician limestone karst in Gujiao Mining Area, a comparison on the field ge ological survey and the hydrological drilling information and the indoor test analysis were conducted. The results showed that a section relative water isolation layer with a first karst aquifer in the middle was individually developed in the roof and floor of the Fengfeng Group. The floor section of Shangmajagou Group was a relative water isolation layer and above the water isolation layer, there were second and third karst aquifers. The backfill type relative water isolation layer at the top of the Ordovician limestone was controlled by the movement of the paleostructure.The karst phenomenon between the strong and weak phases of the Ordovician limestone was controlle d by the lithology rhythm combination.The marlite section became water bearing layer section of the crack karst, due to the salt dome role of the gypsum formation caus ed a layer like gypsum karst conglomerate zone, broken rock zone and crack zone.The study held that 30 m thick backfill type water isolation layer at the top of Fengfe ng Group and marlite gypsum formation at the bottom of the Fengfeng Group could be the water isolation key layer.