Abstract: The oil/water inversion phenomenon has been revealed by recent well drilling aimed at the Carboniferous bioclastic limestone in Bashituopu oilfield in Tarim basin. To interpret the abnormal phenomenon, the fluid connectivity in this reservoir is analyzed by well performance and production data and fluid property correlation, and the petrological characteristic of the reservoir is investigated by core and thin?section observation. And then the reservoir model is developed by research of its abnormal pressure genesis and relations between oil?gas migration and overpressure. It is suggested that in inner regulation of reservoir, it is the mini?overpressure unit and tight zone that overcome the oil?water displacement pressure and block the oil?gas migration toward the top of slope, hence forming the phenomenon of oil/water inversion. Also, the direction and domain of the non?structural oil?gas prospecting in western Maigaiti slope are presented in this paper