Abstract: A new method of continuous measurement of the concentration of ²²⁰Rn progeny without replacing membrane frequently was established based on α spectroscopy. A comparison study between the new method and the standard method for determination ²²⁰Rn progeny reference levels was carried out in the radon laboratory of the University of South China. The results show that under the high level measurement environment of ²²⁰Rn progeny, the relative difference of the two method is 5.0% for ThB and 7.0% for ThC during eight measurement periods. Under the low level measurement environment of ²²⁰Rn progeny, ThB relative difference of the two methods is controlled within 4.5% and that of ThC is controlled at about 10.0% during four measurement periods. The total uncertainty of ThB and ThC is controlled at about 5% for measurement ²²⁰Rn progeny’s level of 100 Bq/m³ in the environment, respectively. The effect of aerosols deposited on the membrane surface on membrane self-absorption can be ignored in the process of sampling. The new method provides accuracy, quick and continuous measurement for ²²²Rn/²²⁰Rn progeny.