210Po has become a non-negligible radioactive safety problem in the fourth generation Lead-based Fast Reactor (LFR) due to its high toxicity and volatility. It will be produced by neutron irradiation of coolant and emits α ray. This may cause potential internal exposure hazards when workers are working in the plant. Polonium produced in the primary coolant circuit of the Reactor will be released to cover gas due to its volatility. This process is slow but not negligible. Therefore, the migration of polonium in the whole reactor and the distribution in the containment room for the M2LFR-1000 was preliminary analyzed. According to the radionuclide migration theory, the migration of polonium was analyzed theoretically, and the distribution of polonium was simulated by FLUENT. Two situations are simulated, one is normal operating condition and the other is leakage accident of covering gas. Preliminary calculation shows that polonium is distributed homogeneously throughout the space with the accumulation of radionuclides only at the certain special place, and the concentrations below safe levels under normal operating conditions. The method of analysis procedure can also be applied to analyze the distribution of other radionuclides.