Abstract: The molten salt reactor (MSR) features convenient fuel fabrication, good neutron economy and flexible fuel management, has and there is the potential to utilize the TRU produced in the spent fuel of the light water reactor directly. The selection of fuel, lattice parameters and fuel/graphite volume fraction has been optimized in this paper. Through the calculating and analyzing the core lifetime of the TRU fueled thermal spectrum MSR, the stock of TRU, MA-fission ratio and TRU-fission ratio, it proves that thermal spectrum MSR can operate for a long period with long refueling cycle, which can reduce the difficulty of online refueling and have a better transmutation ratio of MA and TRU with lower radioactive toxicity.