Net primary productivity (NPP) is an important indicator for vulnerability monitoring in arid ecosystem. Using MODIS remote sensing data and the improved solar energy efficiency, we estimated the NPP of grassland ecosystem of HulunBuir in 2006, and then output from the improved solar energy efficiency model was validated by the field survey data during growing season of 2006. Comparison of estimated NPP and field sampling NPP, the field sampling NPP was greater than estimated NPP, but there was better interdependency between the field sampling NPP and estimated NPP.The total NPP of grassland ecosystem in HulunBuir was 2.9×1013 gC/a in 2006, with an average of 261.01gC/m2•a. The average was the minimum in Xinbaerhuyou Banner, the maximum in Genhe. For the difference grassland types, lowland meadow was the maximum of unit area, the next was alpine meadow, and temperate steppe was the minimum.