Abstract: A method for determination of uranium and nitric acid in uranyl nitrate system was established through combination measurement of density-conductivity-temperature. A mathematical model, which described the relationship between the concentration, temperature, density and conductivity, was obtained. This model was a set of non-linear dualistic quadratic equations. Once the temperature, density and conductivity of uranyl nitrate system were measured, the concentration of uranium and nitric acid could be calculated by computer. The method was used to determine the concentration of uranium and nitric acid in uranyl nitrate system. The results show that the relative errors are between ±5% to uranium and nitric acid.