In order to obtain accurate modal parameters of fuel assembly in the seismic test of fuel assembly, the finite element model of fuel assembly is taken as the research object, and the sine sweep signal is used as the excitation to act on the node of the model. On the basis of the transient dynamic analysis results, the transfer function of fuel assembly is obtained by using proper orthogonal decomposition (POD) method, and the modal parameters of the fuel assembly are identified by the least square iteration method, and the frequency, damping ratio and vibration mode of the fuel assembly in each mode are obtained. The transfer function obtained by this method and the transfer function calculated by single node response are used to identify the modal parameters respectively, and the results are compared with those of numerical calculation. The analysis results show that compared with single point response calculation, POD method can extract the key information of multiple nodes in time and space domain, and the calculation results of modal parameter identification are more accurate. This method can be used to identify the modal parameters of the subsequent fuel assembly test, and improve the utilization of the test data and the accuracy of the test results.