The invention discloses a calculating method for the original water saturation of an oil reservoir and based on sealed coring. The calculating method comprises the steps that by using a sealed coringwell of a region block, the porosity, permeability and saturation parameters of a core are obtained through experimental analysis; combined with region block logging and oil testing data, the originaloil-water interface of the oil reservoir of the research region is determined; an original water saturation calculation model of the oil reservoir is established, combined with analysis data of a rock physics experiment, coefficients in the model are determined through a least square method; by using the porosity and the permeability of core experimental analysis, combined with a logging curve, aporosity and permeability calculation model is established through the least square method; and the original water saturation of the oil reservoir is calculated through the logging data by using theporosity and permeability model, the determined original oil-water interface and the original water saturation calculation model in a new well. The calculating method for the original water saturationof the oil reservoir and based on sealed coring realizes accurate calculation of the original water saturation of the oil reservoir through the logging data on the basis of the physical experiment ofthe sealed coring rock, and can guide logging interpretation and identify reservoir fluid properties.