Abstract: Eddy covariance technique was used to conduct the micrometeorological measurements over three kinds of semi-arid grasslands under three different grazing intensities in Inner Mongolia from 27 July to 10 August 2006. The influence of grazing intensities on the energy and mass exchange between the surface and atmosphere over semi-arid grasslands in Inner Mongolia was analyzed. The main results are listed as following: (1) Grazing reduced the vegetation cover ratio and therefore increased albedo.(2) Grazing decreased the latent heat flux. Although the Xilin River site had the pronounced grazing intensity, its latent heat flux was largest. This indicated that soil water condition was the key factor which controlled the surface energy budget over semi-arid grasslands.(3) The daily average CO2 fluxes at Leymus site and winter grazed site were -1.92 g?m-2?d-1 and 0.73 g?m-2?d-1 respectively, which showed that grazing could make grasslands change from CO2 sink to CO2 source. The Xilin River site was CO2 sink and its daily average CO2 flux was -3.35 g?m-2?d-1. Compared to Leymus site, the Xilin River site absorbed more CO2, indicating that soil moisture was an important factor which influenced CO2 flux exchange over the semi-arid grassland.(4) By decreasing the leaf area index, grazing decreased the photosynthesis capacity of vegetations.