We examined CO₂ flux over an alpine meadow on the northeastern Tibetan Plateau to elucidate how temperature controls the carbon dynamics. The CO₂ flux was measured in a Kobresia meadow at an elevation of 3200m above sea level from 2002 to 2004 using the eddy covariance technique. The alpine meadow was a weak sink of atmospheric CO₂ with net ecosystem production (NEP) of 193 g C m^-2 yr^-1 for 2004, which was about twice of that for the other two years. Both the low ecosystem respiration (ER) and high gross primary production (GPP) contributed the high NEP in 2004. The annual GPP was 34g Cm^-2 and 105 g C m^-2 higher in 2004 than 2003 and 2002, respectively. The lowest GPP of 2002 was clearly due to the low GPP in the autumn season when remarkably high air and soil temperature were recorded. The low ER in 2004 was due to mainly the small ER in the summer period when temperature was much lower than other years. In 2004, the growing season was estimated to be about two weeks longer than the other two years. The advance of growing season in 2004 corresponded well to the temperature elevation in the spring season. Further analysis showed that the day/night difference in soil temperatures was positively correlated to the daily net ecosystem CO₂ exchange. The study suggests that temperature environment plays the major role in the annual variation of NEP in the alpine meadow ecosystem.