Abstract: Grassland yield is the basis of developing stock farming, net primary production (NPP) is an important parameter in determining carrying capacity. Using MODIS remote sensing data and the improved solar energy efficiency model, we estimated the NPP of grassland ecosystem of HulunBuir Grassland in 2006, and then the output from the model was validated by the field survey data during growing season of 2006. The total NPP was 2.9×10¹³ gC in 2006, with an average of 261.01 gC/m². Based on the estimated NPP, it was calculated that the optimal carrying capacity should be 765.41 ten thousands sheep units, compared to the actual carrying capacity of 1838.45ten thousands sheep units, thus the total overloading was 1073.04 ten thousands sheep units. The seriously overloading regions are Arun Banner with 325.45 ten thousands sheep units, Zhalantun City with 270.72 ten thousands sheep units, Morin Dawa Daur Autonomous Banner with 254.71 ten thousands sheep units. The carrying capacity of Oroqin Autonomous Banner, Genhe City and Ergun City is insufficient, thus there is great potential for livestock in those area.