Abstract: An analytical method for the determination of U and Pu contents in MOX fuels based on the liquid scintillator fast neutron coincidence counting method is presented. A Monte Carlo model was built based on the experimental setup to obtain the active and passive coincidence count rates of MOX fuel samples in the range of core block number 12-200. The U and Pu contents in the samples are determined by establishing the scale curves of the passive coincidence count rate versus the effective ²⁴⁰Pu mass, the scale curves of the active coincidence net count rate versus the effective ²³⁹Pu mass, and according to the differences in the contributions of U and Pu to the passive and active count rates. A method is given to simulate the acquisition of conversion factors for each isotope of U and Pu with respect to the effective ²³⁹Pu mass, and the feasibility of the method is verified with test samples.After scaling, the U and Pu contents of the unknown samples (number of cores >20, mass >30 g) were estimated, and the relative error of the samples with the number of cores >32 was less than 10%, which can be used as a reference for the analysis of the data in the quantitative measurement of uranium-plutonium in MOX fuels.