Both nitrogen (N) deposition and livestock grazing are important factors influencing species composition, soil nutrient availability, plant productivity and allocation pattern in grassland ecosystems. However, little is known about their interactive effects on alpine ecosystem carbon cycling process such as ecosystem respiration. In 2010 we started a long-term factorial experiment in an alpine meadow in Damxung County in northern Tibet, China, to examine the interactive effects of N addition and grazing on plant biomass allocation, soil microbial carbon and N and ecosystem CO₂ fluxes. The experiment had two N treatments crossed with two grazing treatments, resulting in a total of four treatments coded as CK (control, no N addition and no simulated grazing), N (with N addition but no grazing), G (no N addition but with grazing) and NG (with both N addition and grazing). For N addition, we added 40 kg N hm^-2 a^-1, and to simulate livestock grazing, we selectively clipped palatable grasses and sedges. We analyzed the available data collected during the growing seasons in 2011 and 2012. Compared with CK, N significantly increased ecosystem respiration by 82% and 72% and soil respiration by 53% and 65% in August 2011 and 2012, respectively, but G had no significant effect on ecosystem respiration or soil respiration. Moreover, ecosystem respiration or soil respiration did not differ significantly between CK and NG, indicating that simulated grazing partially counteracted the stimulating effect of N addition on ecosystem CO₂ fluxes. Compared to CK, N addition stimulated plant aboveground growth by 82% and 84% in August 2011 and 2012, respectively, NG promoted plant root compensatory growth and increased plant allocation to belowground by 127% and 116% in August 2011 and 2012, respectively, and G had no effect on belowground biomass. G inhibited soil microbial carbon and did not affect soil microbial N, while N addition increased soil microbial N and soil microbial metabolic activity. Furthermore, compared to CK, both N and NG treatments increased dissolved organic carbon, while G had no such an effect. The correlation analysis showed that ecosystem respiration and soil respiration were mainly controlled by soil microbial metabolic activity and dissolved organic carbon. Additionally, aboveground biomass was significantly correlated with dissolved organic carbon but not with soil microbial metabolic activity. These results suggest that N addition promotes ecosystem respiration and soil respiration directly by the stimulating effects on soil microbial metabolic activity and aboveground plant production, and that photosynthetic substrate supplied by aboveground plant part may be of great importance for ecosystem respiration and soil respiration. The differential effects of N addition and simulated grazing on ecosystem CO₂ fluxes suggest that exogenous N input can relieve the negative effect of grazing pressure on plant production in the alpine meadow. On the contrary, livestock grazing will suppress the stimulated effects of increased N deposition on ecosystem CO₂ fluxes in the future global change scenarios.