As the only reactor operating with liquid fuel in the fourth-generation nuclear energy system, molten salt reactor (MSR) generates a large amount of nuclides within the fuel, which migrate with the flow of molten salt. Consequently, accurate nuclide information is imperative for ensuring the safety of the molten salt reactor. At present, there are two main kinds of fuel nuclide analysis methods: destructive analysis and non-destructive analysis (NDA). NDA is attractive for its ability to determine the content of key nuclides by measuring their characteristic gamma rays or delayed neutrons. In this study, an experimental method was developed to measure the characteristic gamma rays of 232Th and 233U in ThF4 samples. As a result, the contents of 232Th and 233U, the key nuclides of MSR, were obtained. The TMSR photoneutron source device driven by a 15 MeV electron accelerator is employed to simulate the neutron spectrum of MSRs. Before the experimental study was conducted, FLUKA was used to calculate the activities of samples with various experimental configurations, and the optimal ThF4 sample thickness of 0.5 cm was obtained. At the same time, simulations of detection efficiency and efficiency curve fitting for the HPGe gamma spectrometer were performed, and the detection efficiency function was given. The relationship between the self-absorption factor and gamma energy was obtained, and the influence of sample thickness on the self-absorption factor was also considered.