Abstract: The activity ratio of radon progeny is the ratio of radon short-lifetime progeny (²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi) activity concentration. The activity ratio of radon progeny is one of the most significant parameters in the calculation of radon progeny dose conversion factor, which can be affected by many environmental factors, such as the characteristics of aerosols, ventilation rate and so on. In order to add and update the data of activity ratios of radon progeny in the typical urban environments, and analysis its influence on the dose conversion factor, the field measurement studies were performed in the typical urban indoor and outdoor environments by a portable α spectrometer, and the corresponding radon progeny dose conversion factor was calculated through LUDEP. The results show that the average disequilibrium activity ratio of radon progeny in the typical urban indoor environment is 1∶0.59∶0.58, while that in outdoors is 1∶0.50∶0.67. According to the calculation results through LUDEP, the dose conversion factor in indoor environment is 34.28-34.76 nSv/(Bq•h•m^-3), and that in outdoor environment is 78.11-79.38 nSv/(Bq•h•m^-3).