Atmospheric aerosols can affect the solar radiation reaching the ground, which in turn affects plant photosynthesis and ecosystem productivity, and even regional carbon balance. With the further development of global change, atmospheric aerosols pollution and drought stress coexist in some regions, and the high frequency and long duration of drought stress may lead to the conversion of ecosystems from carbon sinks to carbon sources. However, little is known about whether atmospheric aerosols can increase ecosystem productivity when the ecosystem are under water stress. Therefore, in this study we investigated the effects of atmospheric aerosols on diffuse radiation, light utilization efficiency (LUE) and the gross primary productivity (GPP) of poplar plantation under different water conditions in Beijing. The direct and indirect effects of atmospheric aerosols and ecological factors on GPP were explored by the path analysis method, which used the atmospheric aerosols data from 2006 to 2009 and combined with the radiation and carbon flux data monitored by Eddy covariance system in Daxing poplar in Beijing. The results showed that Beijing's atmospheric optical depth (AOD) had obviously seasonal change characteristics. The AOD was higher in spring and summer than that in autumn and winter, and the AOD was the largest in summer. The atmospheric aerosols had significant effects on radiation and micrometeorological factors. With the increase of AOD from 0 to 3, photosynthetically active radiation (PAR) decreased by 43.63%, diffuse radiation increased by 170%, and the fraction of diffuse radiation increased by 2.55 times, while the relative humidity increased by 48.52% and daily temperature difference increased about 3℃. When the ecosystem was under moisture stress, the atmospheric aerosols had no effect on the GPP. When the ecosystem was under non-moisture stress, the LUE and GPP of poplar plantation ecosystem increased first and then decreased with the increase of aerosol concentration. When the AOD was 1.0-1.6, the GPP was maintained at a high level. When the AOD>2.5, the GPP significantly decreased and less than the GPP of the background atmospheric aerosol (AOD<0.4). The path analysis showed that the indirect effect of atmospheric aerosols on ecosystem productivity of poplar plantation was not significant under water stress, the diffuse radiation had the greatest influence on the GPP, and the atmospheric aerosols could increase the ecosystem productivity by increasing diffuse fertilization effect under non-moisture stress. Overall, the atmospheric aerosols had different effects on poplar plantation ecosystem under different water conditions. The suitable atmospheric aerosols could increase the productivity of poplar plantation ecosystems, while severe atmospheric aerosols pollution (AOD>1.5) led to a decrease in poplar ecosystem productivity under non-water stress conditions.