To reveal the influence of planting artificial grassland on the energy balance of the Three-River Source Region on the Qinghai-Tibet Plateau,the variation of the energy budget and its components of an artificial grassland were studied using eddy covariance and micrometeorological methods.The results showed that the highest daily solar radiation (R_s) and net radiation (R_n) were 33.6 and 19.1 MJ m^-2 d^-1,with annual accumulated values of 6789.4 and 2773.3 MJ m^-2,respectively;the radiation efficiency (R_n/R_s) annually averaged 0.41,with a higher value of 0.54 in the growing season from May to September.The sensible heat (H) and latent heat flux (LE) displayed obvious seasonal variations.H was the lowest in December and increased with an increase of R_s,but decreased in the growing season,appearing the sub-low value in mid July.LE remained relatively low in winter,and increased rapidly in early March,reaching a peak in July.The energy partitioning (average annual LE/R_n,H/R_n,and G/R_n were 0.46,0.45,and-0.13,respectively) was mainly composed of LE and H.There were obviously different patterns of seasonal variations of LE and H,with Bowen ratio (β=H/LE) averages for winter,spring,summer,and autumn of 3.33,0.68,0.42,and 1.29,respectively.Affected by the vegetation leaf area index (LAI),the soil water content (SWC) and vapor pressure difference (VPD),and annual maximum values of both the canopy conductance (g_c) and decoupling coefficient (Ω) averaged 16.22 mm/s and 0.70,respectively,in summer,suggesting that LE was controlled by R_n during the growing season of plants.The average values of Ω were <0.5 in other seasons,indicating that LE was strongly regulated by VPD.The present study suggests that 1)R_n/R_s was relatively low despite the high incident solar radiation in the Three-River Source Region;2) the energy balance component variations were mainly controlled by R_n,LAI,and SWC;and 3) the increased artificial grassland coverage changed the processes and components of energy balance.