Due to population pressure and over-grazing, ecological degradation of the rangeland in HulunBuir becomes more and more serious in past decades. To balance pasture grazing activities and ecosystem sustainability, monitoring grass productivity of the rangelands and livestock carrying capacity are very necessary. Grassland yield is the basis of developing livestock, net primary production (NPP) is an important parameters in determining carrying capacity. Using MODIS remote sensing data, we estimated the NPP of grassland ecosystem of HulunBuir in 2006. The total NPP of grassland ecosystem in HulunBuir was 2.9×1013 gC/a in 2006, with an average of 261.01gC/m2•a. Then we based on the estimated NPP to calculate the optimal carrying capacity which was 765.41 ten thousands sheep units. The actual carrying capacity was 1838.45 ten thousands sheep units, total overloading was 1073.04 ten thousands sheep units. The serious regions of overloading were Arong Banner with 325.45 ten thousands sheep units, Zlantun City with 270.72 ten thousands sheep units, Molidawadahanr Autonomous Banner with 254.71 ten thousands sheep units. The carrying capacity of Oroqin Autonomous Banner, Genhe City and Erguna City were scarcity, there were great potential to excavate in livestock.