In this study, a two-channel thermal dissociation cavity ring-down spectroscopy (TD-CRDS) system based on cavity ring-down spectroscopy technology was established for the rapid and simultaneous measurement of ambient nitrogen dioxide (NO₂) and organic nitrates (ON). NO₂ was directly measured by its absorption at 406 nm, while ON was indirectly measured by the NO₂ product of its thermal decomposition at 450 ℃. The ON conversion efficiency reached 99% at this temperature. The effective absorption cross-section of NO₂ was obtained by the convolution of the high-resolution absorption cross-section of NO₂ using a laser with a central wavelength of 406.02 nm. The laser spectrum was 5.74×10 ^-19 cm ²·molecule ^-1. A stability test of the heating device revealed an optimal flow rate of 1 L/min. The simultaneous measurement of the ambient NO₂ by the NO₂ and ON cavities exhibited good consistency, with the correlation coefficient R²=0.99. After optimization, the detection limit of the system reached up to 2.42×10 ⁹ molecule·cm ^-3 (standard deviation: 3σ; temporal resolution: 1 s). Comparing the TD-CRDS system with the long-path differential optical absorption spectroscopy (LP-DOAS) in terms of NO₂ measurement, good consistency was obtained (R²=0.93), indicating that the system has high measurement accuracy. The TD-CRDS system was applied to field observation, and the time series of NO₂ and ON concentration were obtained.