In this study, the open-circuit eddy covariance system was used to measure and analyze the carbon dioxide exchange (NEE) flux of the sub-alpine evergreen coniferous forest net ecosystem exchange in the Qinghai-Tibet Plateau during the non-growing season. The study area is located in the Hongla Mountain Yunnan snub-nosed monkey National Nature Reserve, belonging to the core area of the Three Parallel Rivers in the Tibet Autonomous Region. The characteristics of CO₂ flux in the non-growing season of subalpine forest and its main influencing factors were further discussed. The NEE value of evergreen coniferous forest in the Nature Reserve is manifested as an obvious ‘U’ curve in the non-growing season. It shows carbon absorption in the daytime and carbon release in the night. The diurnal CO₂ indicated its absorption peak from 12:00 to 15:00, with 10 h average daily carbon sink time. March, February, November, January, and December follow April in the order of monthly NEE during non-growing season. During the study period, meteorological factors, i.e., air temperature (T), relative humidity (RH), saturated vapor pressure deficit (VPD), and photosynthetically active radiation (PAR) had significant effects on carbon exchange. The results showed that forest carbon absorption was sensitive to temperature and the photosynthesis obviously throughout the whole non-growing season. Among the influencing factors, photosynthetically active radiation had the greatest impact on carbon exchange; NEE at night was highly significantly correlated with 5 cm soil temperature (P<0.01) and increased with soil temperature. In the whole non-growing season, NEE, Re and GEE were -596.759 g CO₂/m², 582.849 g CO₂/m² and -1179.608 g CO₂/m², respectively. This subalpine forest ecosystem has obvious carbon sink function in comparison with other ecosystem types on the Qinghai-Tibet Plateau.