High-fidelity modeling and simulation have emerged as a prominent trend in the design and analysis of advanced reactors. The complex structure of components within the core of liquid-fueled molten salt reactors (MSRs) greatly impacts thermal-fluid performance. Consequently, the applicability of high-fidelity computational fluid dynamics modeling and simulation methods is initially assessed. A high-fidelity thermal-fluid model with detailed geometric modeling and accurate power distribution for the Molten Salt Reactor Experiment has been developed, and the simulated results closely align with the designed parameters. The effects of various turbulence models under steady-state conditions are analyzed. Furthermore, several modified core geometries have been proposed to improve thermal-fluid performance and reduce the maximum core temperature. The implementation of modified lattice block structures, along with flow distributors and guide plates, effectively aligns flow distribution with power distribution in the core and leads to better temperature uniformity within the core. The optimization method and these modified geometries provide valuable references for the design and optimization of MSRs.