With remote sensing and climatic data, CASA model was applied to simulate spatiotemporal variations of grassland net primary productivity （NPP） in Inner Mongolia from 1981 to 2001. Impacts of climatic factors and human activities on the grassland NPP were primarily distinguished via statistical analysis. The results showed that from 1981 to 2001, approxmiately 69 of the grassland NPP had no significant change, while about 30 % of the grassland obtained NPP increment and only about 1 %of the grassland experienced a process of NPP decrease. Spatially, the NPP in northeastern, southeastern and southern part of Inner Mongolia significantly increased, but in boundary areas of the desert steppe and typical steppe in the central region of Inner Mongolia, the grassland degraded in term of NPP change. For the whole region, NPP of Inner Mongolian grassland showed a slightly increasing but not statistically significant trendthe long term averaged seasonal NPP between July and August is 192.0 g/m^2 （150.5-255.5 g/m2）. There was a significant positive correlation between NPP and precipitation, but increased temperature had the effect to cause NPP decreasing. The solar radiation in this region showed no obvious correlation with the grassland NPP. Human activities had determinative impacts on grassland NPP on local scale. While grazing strength represented by livestock density intensified during the two decades in Tumote Left Banner and Tumote Right Banner, the grassland NPP there decreased rapidly and remarkably.%利用遥感扣气象数据，采用CASA（Carnegie-Ames-StanfordApproach）模型和统计分析方法，研究了1981～2001年内蒙古自治区草地7-8月植被净初级生产力（netprimaryproductivity，NPP）的时空变化特征，并分析了气候因素和放牧强度对NPP的影响。结果表明，1）1981-2001年，内蒙古草地NPP显著减少、显著增加和变化不明显的面积分别占1％、30％和69％；NPP显著增加的区域位于内蒙古东北、东南和南部，NPP显著减少的区域零星分布于该区中部荒漠草原和典型草原分界处。总体而言，该区NPP增加不甚明显，21年7-8月草地NPP（均以C变化计）平均值为192．0g／m。，年际变化范围为150，5－255．5g／m＾2。2）7-8月降水是该区NPP年际变化的主要驱动因子，降水量高的年份NPP亦高。NPP与气候因素间的关系表现为NPP随降水增多而升高，随温度升高而下降，辐射对NPP的影响不明显。3）综合考虑气候因素与人类活动对草地NPP的影响发现，21年间，土默特左旗和土默特右旗境内放牧强度增加导致NPP显著下降。
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