Abstract: Soil is fundamental to the survival of human, providing food, water and other resources. It is also an indispensable part of global carbon cycle. The estimation of soil organic carbon(SOC)is an important issue in regional carbon accounting. The development of remote sensing technology makes it possible to obtain high spatial resolution and short cycle of large area synchronized ground observation data, which contributes to improve the accuracy of soil organic carbon estimation. This paper measured and evaluated the value of soil sequestration, using remote sensing and a carbon cycle process model, providing references for regional carbon accounting. Based on the CASA model and ecosystem process model, the SOC stocks(top 0-30 cm)of the Guanzhong- Tianshui Economic Region in Shaanxi and Gansu Province, China, was estimated. Using the results, the region's 2014 carbon sequestration value was evaluated using net present value(NPV). The paper also presented the temporal changes and spatial distribution of soil organic carbon sequestration in the study area. Carbon sequestration in the top 30 cm soil in the Guanzhong-Tianshui Economic Region increased by approximately 2.4×10⁷t between 2000 and 2014(levels in 2000, 2005, 2010, and 2014 were 24.19×10⁷t, 24.86×10⁷t, 23.72×10⁷t and 26.59×10⁷t, respectively). The paper examined 6 different carbon sequestration payoff scenarios with different carbon prices and discount rates. From the perspective of carbon sequestration across different land use types, it was found that the average NPV of forestland was greater than grassland, which was greater than other land types and cultivated land. The total value of cultivated land, however, was greater than grassland, forest land, and other land types. In addition to physical and chemical properties, the unit area sequestration values of soil are also affected by the climate factors such as precipitation and temperature．Besides, setting up reasonable carbon price and discount rate will be a effective way to adjust the earning of soil carbon sequestration.

Key words: soil carbon pool, process model, soil basal respiration, net present value, Guanzhong-Tianshui Economic Region