Abstract: In order to study the effects of global climate change between carbon dioxide continuous interaction and water vapour of the farmland ecosystem in arid and semi-arid region, during January 2009 to December 2009, applying eddy covariance system (EC) continuous observing the variations of water vapor flux and CO₂ flux at the atmosphere land interface of underlying surface (bare soil and different growth periods) of cotton field ecosystem in Wulanwusu, the author analyzed the seasonal and diurnal variations of water vapor flux and CO₂ flux. The results showed that: (1) the annual CO₂ flux of the underlying surface of oasis cotton ecosystem was divided dry and wet seasons, the underlying surface of cotton field absorbs CO₂ mainly in dry season, wet season to release the CO₂ mainly, but the annual uptake was much larger than the amount released. (2) In the wet season, CO₂ fluxcurve of the underlying surface of oasis cotton field ecosystem showed upward opening parabola, was better correlative to the underlying surface cotton field development. (3) Water vapor flux of the underlying surface of oasis cotton field ecosystem was segmented into 3 phases yearly, according to water vapor flux from small to large phases were separated to the covered with snow stage, the bare soil stage and the cotton-growing stage. (4) In the wet season, the diurnal variation of water vapor flux of the underlying surface of oasis cotton ecosystem was obvious, was better bound up with sunshine intensity and temperature.