Abstract: Recognize the problem of agro-ecosystem CO2 sources or sinks from multi-angles helps draft correct agricultural management policies, by cutting down carbon emission and increasing carbon reservation, to help China take initiative in output author; Research state about carbon cycle in farmland and normal observation methods of internal and external were introduced detailed in this essay; Merits and demerits analysis were measured by several routine methods, such as eddy covariance method, static opaque chamber method, static transparent chamber method. The search advances on farmland CO2 flux estimation in Europe and America were proposed, method and ways to improve the accuracy of carbon exchange measurement in farmland have been raised in this essay; Finally, in accordance with the realities and necessities of agro-ecosystem flux research in China, some suggestions and prospects were put forward.