The data of seismic interpretation,paleontology,drilling-geology,geochemistry and etc adequately prove the existence of Caledonian Movement and corresponding paleo-karstification in the north area of the Tarim Basin.This paper discusses the control factors such as paleo-karstification,property of primary rock,grade of fracture,paleo-physiognomy,palaeoclimate,paleo-hydrology and so on.Lithology,Sr isotope and inclusions all helped us figure out the characteristics of Caledonian atmosphere fresh water eluviation.Early fault and accompanying fractures are the main control factors in the mid-Caledonian karstification and their distinctive features are as follows:1) strata-bound with extensive area and a low depth,and well-developed 0 to 35 meters below p unconformity;2) fault-controlled,with bigger dissolved cavern near the fault;3) greater heterogeneity of effective reservoir.Thus it is predicted that the areas of favorable reservoir rocks would be distributed around stacked sites of erosional areas of paleoweathering crust and areas of Caledonian faulting e.g.the plunging crown of the axial zone of the Akekule anticline and the NE-and nearly N-Striking fault zones in the southwest and southeast parts of the Tahe oilfield.Discovery and occurrence of paleo-karstification is of great significance to the oil exploration in the sourthern aprt of the Tahe oild field.