Abstract: The paper respectively adopted physiochemical properties of every soil stratum from² 473 soil profiles of the second soil survey. The corresponding carbon content of soil is estimated by utilizing conversion coefficient 0 58. First, we calculated the carbon content of every stratum of different soil stirp in the same soil subtype. Then, we took soil stratum depth as weight coefficient to acquire the average physiochemical properties of various kinds of soil stirp. Finally, we got the average depth, organic content, duck density and carbon density of different soil subtypes through area averaging. The total carbon quantity of different kinds of soil can be calculated by the following expression: C j=0 58S jH jO W j where j is the soil type, C j is the carbon storage of j soil type, S j is the distribution area of j soil type, H j is the average depth of j soil type, O j is the average organic content of j soil type, and W j is the average bulk density of j soil type. In the second soil survey, the total amount of soil organic carbon is about 924 18?10 8 t and carbon density is about 10 53 kgC/m² in China according to the statistic country area 877 63?10⁶hm². The spatial distribution characteristics of soil organic carbon in China are that the carbon storage increases with the increase of latitude in eastern China and the carbon storage decreases with the decrease of longitude in northern China. There is a transition zone where carbon storage varies greatly in China. Moreover, there is an increasing tendency of carbon density with the decrease of latitude in western China. Soil circle has implications on global change, but the difference in soil spatial distribution is substantial in China. Because the structure of soil is inhomogeneous, mistakes will be resulted in estimating soil carbon reservoir. It is thus necessary to farther resolve soil respiration, organic matter conversion and others related problems, and build uniform and normal methods of measurment and sampling.

Key words: terrestrial ecosystem, global change, soil carbon reservoir, carbon cycle