Abstract: For precise exploitation of oilfield in the middle-late stage and further adjustment and potential tapping, it is urgent to carry out more detailed study on reserves, among which the most important is vertical subdivision of computing units. For multilayer structural reservoir, the vertical subdivision is based on the distribution characteristics of interlayers and physical properties of single layer within the oil formation, taking single layers or layer combination with similar distribution characteristics or physical properties and continuously distributed vertically as computing units. According to the theoretical deduction of reserve optional parameters before and after the vertical subdivision of computing units, combined with the sedimentary distribution characteristics of reservoir, it is considered that when there is no reservoir pinch-out within the oil-bearing area, only the average effective thickness of reservoirs with large difference in the plane reservoir thickness are reduced. In the case that the reservoir is pinching out, the reservoir parameters of normal delta sedimentary reservoirs generally decrease; while the average effective thickness of braided river delta sedimentary reservoir decreases, and the average effective porosity and average oil saturation increases. The conclusions can effectively guide the vertical subdivision of computing units in reserves evaluation and provide technical support for the study of precise reserves in similar oilfields.