In the process of water displacing oil, the relationship between resistivity and water saturation is the fundament of the quantitative research on the waterflooded grade and the remaining oil saturation with well logging data. A large number of core analysis data and production data are cumulated in the process of oil field exploitation, which offers the basis for the above research. This paper educed two methods from the Archie equation and material balance theory to calculate the quantitative relationships between R _z and S _w, and between R _t and S _w. The relationships set up by the two methods are similar to those set up by the real core measurements. The results can be used to analyze influencing factors and determine saturation quantitatively.