Clastic rock reservoir is the main reservoir type in the oil and gas field. Archie formula or various conductive models developed on the basis of Archie’s formula are usually used to interpret this kind of reservoir, and the three-water model is widely used as well. However, there are many parameters in the threewater model, and some of them are difficult to determine. Most of the determination methods are based on the statistics of large amount of experimental data. In this study, the authors determine the value of the parameters of the new three-water model based on the nuclear magnetic data and the genetic optimization algorithm. The relative error between the resistivity calculated based on these parameters and the resistivity measured experimentally at 100% water content is 0.902 4. The method studied in this paper can be easily applied without much experimental data. It can provide reference for other regions to determine the parameters of the new three-water model.