We analyzed the vertical long distance migration experiment data of radon and its daughters,and found that the number of α particles is insufficient to explain the fast upward migration of radon by helium- radon clustering. If assume that radon has very strong ability to adsorb the helium from the air to form helium-radon clusters for vertical migration, then there is an inconsistency between the tentative and that experimental conclusion,that the upward and downward migration probability of radon and its daughters in natural state is equal to that when helium gas is added.So we propose that helium- radon clustering may not be the main reason of radon and its daughters′ fast upward migration. There may be other more complex reasons. The phenomenon needs further research.