Abstract: The thermal fluid phenomena of the core of the pebble bed fluoride salt-cooled high-temperature reactor were researched. By using the CFD method for 3D modeling and computing, the pebble surface temperature distribution of the fuel, and the velocity field, the temperature field and the pressure distribution of the coolant of the reactor core were gotten. The capacity of the fluoride salt to cool reactor core in the steady condition was verified, and the influence of the special thermo-fluid mechanics property for the fluoride salt on core safety was analyzed. The results can be used in the primary design for fluoride salt-cooled high-temperature reactor.