Abstract: One of the key techniques of building a calibrating and experimental device (thoron chamber) for thoron and it’s progenies monitors is the determination method of thoron and thoron daughters concentrations, especially in radon and thoron mixed (atmosphere.) A air-flow and time-delay method for the simultaneous measurement of (radon) and thoron reference concentrations in thoron chamber was developed in Radon Laboratory of Nanhua University. The monitoring device mainly consists of two scintillation cell measuring equipments and a time-delay equipment with the volume of 24 L. When the radon and thoron mixed gas flows through the monitoring device with the flow rate of 3 L·min~(-1), the scintillation cell monitoring equipment after the time-delay (equipment) measures radon reference concentration in thoron chamber, and the another scintillation cell monitoring equipment before the time-delay equipment can measure thoron reference concentration in thoron chamber after deducting the contribution of (radon.) The uncertainties of the calibration factors of the scintillation cells for radon and thoron concentration measurement by air-flow method are less than 5.0%.