Abstract: Neutron fluence irradiation goal of graphite material of solid fuel thorium molten salt reactor is 5×10²⁰cm^-2（±15%）（E＞0.1 Me V, relatively temperature 650℃±50℃）. An irradiation experiment was carried out to assure irradiation condition. The assembly of graphite material is modularized designed which is composed of the sealed part, the irradiation part, and the gas cooling system. The neutron fluence was calculated by MCNP code, and neutron indicators were installed in the graphite irradiation assembly so well. The irradiation result shows that the gas cooling system maintained the assembly temprature a little higher than the upper limit, and the MCNP method served well in neutron fluence calculating of graphite material irradiation in HFETR.