Abstract: Coconut shell activated carbon is widely used as adsorption material for radon, iodine and other radioactive gas. In order to improve the adsorption efficiency of coconut shell activated carbon to radon, coconut shell activated carbon was modificated by liquid nitrogen immersion, simultaneous liquid nitrogen immersion and evaporation and low temperature nitrogen washing. The results show that the modification method of simultaneous liquid nitrogen immersion and evaporation is the best, the adsorption coefficient of modificated activated carbon after contineous liquid nitrogen immersion and evaporation for four times is improved by 36% than that of unmodificated activated carbon, improved by 15% for modificated activated carbon after liquid nitrogen immersion, and low temperature nitrogen washing modification has no effect. The BET measurement results show that the radon adsorption capacity of modificated activated carbon is obviously positive correlation with increase of micropores with pore size of 0.54 nm. Liquid nitrogen modification method has the advantages of simple, short period of modification, low cost and so on.