Dinitrogen pentoxide (N₂O₅) is the most important active nitrogen species at night, and accurate detection of it is important for understanding chemical processes in the atmosphere at night. The high precision cavity based cavity ring down spectroscopy (CRDS) and cavity-enhanced absorption spectroscopy (CEAS) have become the most popular methods for N₂O₅ detection due to their high sensitivity and fast response time. However, N₂O₅ has the characteristics of high activity and easy loss, which affects the measurement accuracy of it. In order to ensure the accuracy of N₂O₅ measurement in the field by the N₂O₅-CRDS detection system, a set of device for on-line stable synthesis of N₂O₅ standard source was developed in this work, which can generate stable concentration of N₂O₅ by controlling the reaction of O₃ and NO₂, and then, the transmission efficiency of N₂O₅ gas in the N₂O₅-CRDS detection system was further studied. The transmission efficiency of N₂O₅ in perfluoroalkoxy alkane (PFA) sampling tube (length 3 m, outer diameter 6.35 mm) , Teflon film holder (filter with 5 μm PTFE) and heated PFA tube (outer diameter 12.7 mm) were investigated, and finally the total transmission efficiency of N₂O₅ was obtained as 86.74% based on the system parameters used infield observation. The comparison results show that the transmission efficiency measured by this method is in good agreement with the calibration results of other works, which verifies the validity of this method.