Continuous online measurement of atmospheric CO_2 is an important foundation for research on global and regional carbon cycles as well as their climatic and environmental effects. From March 2012 to February 2013,atmospheric CO_2 concentrations were measured continuously at Menyuan Atmospheric Background Station with a non-dispersive infrared absorption spectrometer system. This is the first time such measurements have been made in an alpine meadow region on the Tibetan Plateau. The analysis results showed that: 1) The CO_2 time series showed remarkable fluctuations. Approximately 59% of observed values were filtered as background data. The average value of CO_2 background concentration was 391.2 * 10 - 6,which was lower than the global average in the year 2012 (393.1 * 10 - 6).25% and 16% of observed values were filtered as non-background data,being influenced by sources and sinks,with average values of CO_2 non-background concentrations of 401.1 * 10 - 6 and 380.7 * 10 - 6,respectively. 2) The highest variation amplitude of hourly concentration in a day reached 28.9 * 10 - 6 in the summer. The highest hourly average concentration was observed at 08: 00,07: 00,08: 00 and 11: 00 in the spring,summer,autumn and winter,respectively,with the lowest hourly average concentration observed at 16: 00 in all the seasons. 3) The atmospheric CO_2 concentrations in Menyuan clearly varied seasonally,with the maximum value of 397.7 * 10 - 6 in January and the minimum value of 381.0 * 10 - 6 in August. 4) Higher measured CO_2 concentrations were associated with winds from the W-NW-N direction in the spring,summer and autumn, while from the SE-S-SW direction in the winter. The seasonal variation characteristics of CO_2 concentrations in Menyuan were due to the combined impacts of of the seasonal variation of sources and sinks,as well as the surface wind.