Abstract: To understand the processes and mechanisms of soil-vegetation-atmosphere interaction in Inner Mongolia semi-arid grassland, a project named “Inner Mongolia Semi-arid Grassland Soil-Vegetation-Atmosphere Interaction (IMGRASS)", which is supported by the National Natural Science Foundation of China (NSFC) as a major project, has been conducted in 1997-2001. Within IMGRASS, a coordinated meso-scale field observation was conducted in growing season of 1998. The experi mental sites are located in Xilingol semi-arid grassland. The surface types include Xilingol typical steppe and Sandy Land Hunshandake, a kind of mid-latitude savanna. The topography is Mongolia plateau with mild complex terrain. The coordinated observation is consisted of related parameters as surface and boundary layer meteorological parameters, surface sensible and latent heat flux, N2O, CH4, and CO2 flux of the surface, radiation flux and precipitation at four core stations and other sites with simultaneous vegetation and soil parameters. In addition, remote sensing observation and GHG flux observation were made in certain sites during 1999-2003, including specific observation for dust aerosols in spring 2001. Based on field observation and regional climate data, process analysis and numerical simulations were made for various characteristics of land surface atmosphere coupling of mid-latitude semi-arid grassland, long-term variation of grassland ecological-climate interaction, impact of human activities to ecology and desertification were and made. Short summary about the project and the preliminary results are presented.