Abstract: Ordovician oil reservoir of Tahe oilfield is the largest fractured carbonate rock reservoir ever found in China. The reservoir is strongly heterogeneous and difficult for building reservoir model. The parameters are also uncertain for estimation of reserve. Tahe oilfield adopted the static volumetric method to calculate geological reserve in the initial exploration and development stage. The result from calculation of reserve is not in line with the conclusion drawn from later development stage of the oilfield. In the light of different exploration and development stages, this paper compares and analyzes a series of calculation methods, such as static volumetric method, improved volumetric method, dynamic method, probability method, and fracture-cavern unit method and their adaptabilities. It is pointed out that types of reservoirs should be divided according to soluble cave type, porous type and fracture type. Area, one of the parameters, is determined through limit value set by seismic amplitude variation, thus determining the oil-bearing area. The result is line with the conclusion drawn from the current development.