Abstract: The study of differential distribution of WOC is meaningful for understanding the geologic features of the reservoir, evaluating accurately the reserves of an oilfield and improving the oilfield development. The Shuanghe Oilfield is located in the Southwest of the Biyang Depression of the Nanxiang Basin,at the plunging part of a southeast-northwest axis nose structure. The oildom A of the Block 438 is a nose structure reservoir in the monolayer of H₃Ⅲ₁¹. It is found during the oil field development that the WOC depth is different in different places. So far the phenomenon has not been well studied. We studied in this paper the mechanism of the differential distribution of WOC from the perspective of oil pool-forming dynamics with reservoir research data. According to the dynamics of oil and water differentiation, the distribution of WOC is controlled by physical properties of reservoir, dip of strata and the density of crude oil. The physical properties of reservoir, dip of strata remain same in the region. Therefore, the difference of oil column height, or the differential distribution of WOC, is mainly affected by physical properties of the reservoir.