Atmospheric CO₂ concentrations had increased from approximately 280 μmol/mol  in the late 19th-century to over 360 μmol/mol  today. Elevated CO₂not only pricked up global greenhouse effect, but also changed the C balance of global ecosystems, which led to the changes of ecosystem structure and function. Alterations in microbial mineralization and nutrient cycling may control the longterm response of ecosystems to elevated CO₂. Elevated CO₂concentrations influenced carbon cycle, ecosystem productivity, plant, soil, microbe, and other environmental factors. The effects of elevated CO₂ on growth were highly dependent on interactions with N cycling. Particularly important was the effect of elevated CO₂ on N cycling and availability because shortages in N could eventually attenuate the increased plant biomass production seen in shortterm elevated CO₂ studies. Changes in microbial biomass C and N, microbial activity and inorganic N could indicate the effects of elevated CO₂on N dynamics. Increases in N-use efficiency tended to increase the C/N ratio of plant materials grown in elevated CO₂. The purpose of this paper  is to summarize the changes of ecosystems and C-N coupling due to the increasing atmospheric CO₂concentration in order to lucubrate to carbon cycle and nitrogen cycle in arid and semi-arid region.