To achieve accurate measurement of 220Rn activity concentration by using radon monitor, this study was carried out theoretically and experimentally. Using high emanation rate, stable and the activity are 17.1 Bq,64.0 Bq 220Rn solid source to provide different 220Rn activity concentration. The cavity sensitivity of radon monitor measuring 220Rn and the impact of sampling pump flow rate to relative sensitivity was discussed. The result shows that sampling flow rate and source activity has little to do with the cavity sensitivity of radon monitor,...