Made the Populus euphratica communities as the research object in the extreme drought environment the CO₂ flux characteristics and water use efficiency(WUE)during different phenological phases of P. euphratica were studied using the eddy covariance flux observation system. The results showed that the daily variations in the CO₂ flux trends were basically identical in different phenological phases of P. euphratica,but there were obvious seasonal differences. The change amplitude ofchange in CO₂ flux rate at the maturity stage was the largest,and was the smallest at the flowering stage,and medium at the foliation stage. Correlation analysis showed that the CO₂ flux rate of P. euphratica community was significantly correlated with the sensible heat flux,latent heat flux,momentum flux,soil heat flux,net radiation and relative humidity of the air. Among them,net radiation,and latent and sensible heat fluxes were more highly related with the CO₂ fluxs,The scope of change,i.e,-0.82--0.88、-0.64--0.66 and -0.63--0.94,respectively,the main environmental factor affecting the CO₂ rate of the community. Thus this study shoued an obvios daily change in water use efficiency of the P. euphratica community. The dynamic performance of WUE of the community time was as follows:water use efficiency varied greatly at the flowering stage,leaf coloration stage,and defoliation stage,and was the highest at the flowering stage,most stable at the foliation and maturity stages. Two of the most critical factors affecting the communities were net radiation and wind speed.