On the basis of theoretical analysis, this article describes the experiment of the absorption of Radon 222 Rn and Thoron 220 Rn in air on active charcoal under condition of varying humidity and temperature. The result of experiment shows that, under the condition of lower humidity, the absorption of 222 Rn reduce as the temperature raises. Since the half life of 220 Rn is short, the influence of the temperature is small. But as the relative humidity raises, the absorption of 222 Rn and 220 Rn reduces significantly.