Abstract: Based on an advanced concept of thorium molten salt reactor (TMSR) which applied a fuel composition without BeF₂ and solid BeO moderator, key lattice parameters including lattice dimensions, P/D (ratio of lattice pitch to channel diameter) and ²³³U content were optimized through varies scheme analyses. SONG/TANG-MSR, an inhouse developed computer code system, was employed in the optimal design of TMSR. Adopting a small pitch size and rather low ²³³U content, an advanced TMSR achieved a high breeding ratio and maintained a negative power coefficient as well according to computation results. Compared with traditional MSR, the advanced TMSR is better in breeding nuclear fuel. With these lattice parameters, the advanced TMSR meets the requirements of next generation nuclear power systems on safety and sustainability.