This paper introduces the construction background and structure of the metrological verification system of seismic radon observation instrument,namely,the radon chamber which possesses the advantages of real-time monitoring of radon concentration,dynamic radon supplement,adjustable expected value of radon supplement and stability. Through the radon leakage rate experiment and four-round radon supplement experiment,this paper concludes that the radon leakage rate of the radon chamber is up to 0.0001393Bq/min and the radon incidence rate reaches 23.35Bq/min. According to the technical requirements of JJG 825-2013 Verification Regulations for Radon Measuring Instruments,the stability of radon chamber is better than 5% in the 8-hour verification stage of 800Bq/m3,1500Bq/m³,3000Bq/m³,6000Bq/m³ and 15000Bq/m³,and also better than 5% in the 72-hour verification stage of 6000Bq/m³,which meets the requirement of radon chamber measurement standard in National Metrology Technical specification.