Based on extensively collected data, we used average carbon density method to estimate 17 vegetations carbon reserve of alpine grassland ecosystem and analyzed its spatial distribution in Tibet. The results indicated that: 1)the total area of all 17 grassland vegetation was 8205.194×104hm2, total carbon reserve was 189.367 Tg (1TgC＝1012g), average carbon density was 2307.895 kgC/hm2，there was significant variation between 395.977~20471.161kgC/hm2 among different grassland types. 2) In the view of grassland types, Alpine grassland and Alpine meadow took the biggest portion of 70.210% all of Tibet grassland. They were also the main grassland carbon reserve in Tibet, and occupied 79.393% of the total.3) In the spatial configuration, the vegetation carbon density gradually decrease from southeast to northwest in Tibet, This distribution is in correspondence to the particular precipitation and temperature in Tibet. Vertical distribution was different according to regions, but alpine meadow or Alpine desert had the lowest carbon density and was characterized by “reach the same goal by different routes”.