Abstract: The radon dynamic adsorption coefficients (DAC) of four types of activated carbons measured in radon room are different from each other. The pore structures (specific surface area, pore size distribution, pore volume, etc.) influence the adsorption ability significantly. Physical adsorption of inert nitrogen was used for evaluation pore structures of those four activated carbon samples. The results show that activated carbon with specific surface area about 800 m²/g has the strong adsorption ability to radon and when the specific surface areas are close, the adsorption ability to radon increases with the micropore specific surface’s percentage. Pore size distribution (PSD) was calculated by H-K, BJH and density function theory (DFT). The micropore size distribution calculated by H-K method shows that pore with size between 0.7-2 nm plays the most important role for adsorption of radon. Mesopore size distribution calculated by BJH method and DFT method shows that mesopore distribution with discrete peaks is more useful to help radon adsorption on activated carbons.