The actually measured data of the formation pressure show that the abnormal high pressure is obvious for Paleogene system of Shizigou Oilfield in Qaidam Basin and the pressure coefficient can reach 2.07 at most. The studies prove that the main causes of abnormal high pressure are due to disequilibrium compaction, hydrocarbon generation from organic matters and tectonic compression. The contributions of the abnormal pressure induced by these three factors are 20%-30% , 30%-40% and 35% -50% respectively of the present remained pressure. In addition, based on the main controlling factors and time order of the abnormal pressure generated in the geological history, the conceptual model of abnormal high pressure in the study area can be established as followings: ( 1 ) low overpressure initially appears in the formations resulted from the disequilibrium compaction, and later a much better closed system generated in the deep part just because of the effective combination of pretty thicker pelite, overlying gypsolyte and faults in time and space ; (2 ) with the rise of fast buried depth of the formations, the organic maters gradually mature and generate hydrocarbon, and finally these conditions become the main source for inner supercharging; (3 ) the continuously increased and gradually strengthened tectonic compression have further enhanced the degree of lhe almurmal pressure.