Global warming is currently one of the most significant global environmental issues.The construction of important carbon sequestration areas (ICSA) is an important way to address global climate change.Using GIS spatial overlay analysis and taking the forest and grassland ecosystems as the study objects,this paper selected three factors,which included the spatial distribution of typical terrestrial ecosystems in the year 2000,the latest research results of carbon sequestration and government documents,to define the location of ICSA of typical terrestrial ecosystems all over China (the study area does not include Hong Kong,Macao and Taiwan).The results indicated that terrestrial carbon pool,carbon sink and carbon sequestration potential are the key indices to constructing an assessment index system of ICSA.The determining process mainly included the following steps: (1) a reasonable selection range was given; (2) the highest value areas of terrestrial carbon pool,carbon sink and carbon sequestration potential were determined; (3) the location of ICSA was defined; and,(4) the nominative method of each ICSA was provided.Twenty ICSAs including forest ecosystem and grassland ecosystem were defined,with a total area of 285.6 * 10~4 km~2.Twelve forest ecosystem ICSAs were distributed in mountainous and hilly areas of the northeast,southeast and southwest regions of China,and the other 8 grassland ecosystem ICSAs were distributed in mideastern Inner Mongolia Plateau,mountainous areas of northwest Xinjiang and southeast Tibetan Plateau.The 20 ICSAs accounted for 29.8% of Chinese territory.However, they can protect 40.7% of the total NPP values of China, and their carbon sequestration capacity is 1.37 times the average carbon sequestration level of terrestrial vegetation in China.Therefore,the results are in conformity with the principle of 'smaller areas get larger ecosystem services'.The ICSAs can be regarded as priority conservation areas to achieve the carbon emission reduction target in China.