Abstract: The resistivity of mixed liquid in a water-flooded zone of an oil field developed by water injection is an important parameter for calculating residual oil saturation,but the existing independent parallel conductivity model and fully-mixed conductivity model for calculating the resistivity of mixed liquid in water-flooded layer have not been verified by experiments. Therefore,the independent parallel conductivity model has been improved by simulating core oil displacement tests on the basis of verifying the mixed state of injected water and primary bound water during water-flooding,which is in between the separate state and fully mixed state,and used the test data to fit the relationship between the resistivity of a mixed liquid and the current water saturation.Combined with the Indonesia Equation,a mathematical model for resistivity and water saturation of mixed liquid in water-flooded layers has been established to solve.By using the newly established mathematical model,the resistivity and water saturation of mixed liquid in water-flooded layer in the Well X of W Oilfield have been determined.The results showed that the water saturation determined by the modified parallel conduction model coincided well with the analytical results of close coring,with the average absolute error as -0.3%,the calculation accuracies of the new techniques were improved significantly compared to those determined by the independent parallel conductivity model and a fully-mixed conductivity model. Since the water saturation was determined in terms of the resistivity of a mixed liquid,it was concluded that the calculated accuracy of resistivity in water-flooded layer was also improved significantly.Relevant research results indicated that the modified parallel conductivity model could accurately determine the resistivity and water saturation of mixed liquid in water-flooded layers of oilfields which were developed by water flooding,and which could be developed more extensively in the future.