Abstract: The pebble bed fluoride salt cooled reactor uses spherical pebbles as fuel and high-temperature molten salt as coolant. The heat source distribution in the reactor is significantly different from that of the pressurized water reactors. Compared with the high-temperature gas-cooled reactor which also uses the pebble fuel, the heat rate of coolant is higher, since the neutron and gamma deposit more energy in the molten salt than in the gas. Therefore, accurate calculation of the heat rate distribution in the reactor is of great significance for the thermal-hydraulic design, transient analysis and structural mechanics design of this new reactor. In this paper, the Monte Carlo calculation code MCNP was used to calculate the heat rate distribution in the 10 MW Solid-fuel Thorium Molten Salt Reactor (TMSR-SF1) designed by the Chinese Academy of Sciences. By using photon-production bias card (pikmt), after three MCNP transport calculations, the total heat rate, volumetric heat rate distribution and maximum volume heat rate for various regions of TMSR-SF1 at beginning-of-life (BOL) and end-of-life (EOL) reactor were obtained. The results show that the heat rate of the fuel pebbles accounts for more than 94% of the total heat rate in the reactor, while the heat rate of the molten salt and reflector accounts for more than 1% of the total heat rate, and the proportion of heat rate of other components in the reactor is less than 1%. At EOL, the heat rate of the fuel pebbles, the control rod and the graphite pebbles decreases, while that of other components such as the reflector increases.