In recent years, significant amounts of oil and gas have been produced from the fractured basement reservoirs such as offshore in Vietnam. These reservoirs are quite different from conventional types of reservoirs, and the fractured basement hasalmost zero matrix porosity while its fracture has high permeability.In these reservoirs, production of the hydrocarbon occurs only through the interconnected fracture networks.In the fractured basement reservoirscontacted with bottom or edge water aquifer, early BT problem as well as abrupt change in production may arise. This increase in water production leads to higher operating cost for water treatment and maydeteriorate both the depletion mechanism and the recovery factor by the bypassed oil. In this study.STARSof CMG is used to investigate the water BT phenomenon in the fractured basement reservoir with the bottom water aquifer by applying 10 -8 cm 2of permeabilityon the cells representing the fractures. In order to examine factors affecting the water BT,simulations with various oil production rates, sizes of bottom water aquifer, and inclusion of capillary pressure of fracture have been conducted. Also, by injecting the water at the top layer of the system with bottom water aquifer, we investigated the water BT phenomenon.Based on the simulation results, we conclude that DFN method is necessary to analyze water BT phenomenon at the fractured basement reservoir.