Abstract: Dose caused by environmental radon progeny is approximately estimated mainly by using the environmental radon exposure and the recommended equilibrium factor of radon and radon progeny. However, environmental conditions vary greatly in different places, and therefore the equilibrium factor of radon and radon progeny also vary greatly, and the estimation method results in a big estimation error. To improve the quality of the dose caused by radon progeny estimated based on radon exposure, it is necessary to measure the equilibrium of radon and radon progeny in typical places. By adopting the NRL-Ⅱcontinuous radon monitor and NR-200A continuous radon daughters monitor developed by the University of South China, the equilibrium factors of radon and its daughters in the air are measured in fields including Qinshan Nuclear Power Base, Hunan Xiangya Hospital, Hunan Provincial Tumor Hospital and Jinyuan Uranium Industry Company. The results show that the equilibrium factors of Radon and its Progenies in coastal areas and Radiation Therapy Center was 40% less than the recommended value. The regional equilibrium factors of Radon and its Progenies in some fields with good ventilation and air purification measures are even smaller, and the equilibrium factors of radon and its Progenies in the indoor environment of inland provinces are similar with the recommended value.

Key words: radon, radon progeny, equilibrium factor