In this paper,the alpine grassland carbon density and carbon reserve in northern Tibet was calculated by field investigation and reference review.The results showed that,1) The total area of alpine grassland in northern Tibet was about 39.059×106 hm2,The carbon density of aboveground and belowground vegetation were 12.158±4.7 g·m-2 and 84.458±20.38 g·m-2,the carbon reserve of aboveground and belowground vegetation were 5.171±0.95 Tg and 25.223±2.96 Tg,the total carbon reserve of alpine grassland was 30.394±3.91 Tg.2)These distributions were different in different grassland groups,the lowest carbon density was Gramineae group and its carbon density of aboveground and belowground vegetation were 6.13±1.51 g·m-2 and 26.04±5.8 g·m-2,the highest aboveground and belowground vegetation carbon density was shrub with hypo-shrub group were 31±3.4 g·m-2 and 244.59±6.9 g·m-2.The highest aboveground and belowground vegetation carbon reserve was Cyperaceae and the amount were 2.24±0.32 Tg and 9.52±0.89 Tg,the lowest carbon reserve was hypo-shrub and were 0.012 4±0.002 Tg and 0.098 1±0.002 Tg.3)this diversity was also observed in all of counties and boroughs,higher carbon density counties were Geji,Zhada,Geer,Cuoqin,the vegetation carbon density respective was 1.76,1.47,1.11 and 1.06 times in average northern Tibet carbon density,and the carbon reserve concentrate in Shuanghu,Zhada,Nima,Ritu,Geji,Gaize,in this area total carbon reserve was 25.2±2.31 Tg,which consists about 82.95 of carbon reserve in Northern Tibet.