The production of radionuclides 90Sr and 131I in molten salt reactors is an attractive option to address the global shortage of radionuclides. This study evaluated the production characteristics of 90Sr and 131I in a modular molten salt reactor, such as equilibrium time, yield, and cooling time of isotopic impurities. The fuel burn-up of a small modular molten salt reactor was analyzed by the Triton module of the scale program, and the variation in the fission yields of the two nuclides and their precursors with burn-up time. The yield of 131I and 131Te has been increasing during the lifetime. 131I has an equilibrium time of about 40 days, a saturation activity of about 40,300 TBq, and while 131Te takes 250 min to reach equilibrium, the equilibrium activity was about 38,000 TBq. The yields of 90Sr and 90Kr decreased gradually, the equilibrium time of 90Kr was short, and 90Sr could not reach equilibrium. Based on the experimental data of molten salt reactorexperiment, the amount of nuclide migration to the tail gas and the corresponding cooling time of the isotope impuri-ties under different extraction methods were estimated. Using the HF-H2 bubbling method, 3.499105 TBq of 131I can be extracted from molten salt every year, and after 13 days of cooling, the impurity content meets the medical requirements. Using the electric field method, 1296 TBq of 131I can be extracted from the off-gas system (its cooling time is 11 days) and 109 TBq of 90Sr. The yields per unit power for 131I and 90Sr is approximately 1350 TBq/MW and 530 TBq/MW, respectively, which shows that molten salt reactors have a high economic value.