Abstract: In this paper the water coning into a well partially penetrating a naturally fractured reservoir under bottom water injection is examined by means of a fixed stream tube model.The generation and development of a water cone in the fractured system and an associated water cone in the matrix system as well as the whole water-cut process of the well aze presented.A clear-cut coning surface and ttze saturation distrilautions both era the surface anti inside of the cone are obtained.The mechanism of both the slcaw arise of the water-oil contact and the xapid water coning into a well axe revealed.Finally,a method to calculate the time-dependent critical production rate is given.All these results can,hardly be obtained by the conventional numerical reservoir simulation technique.