Based on the data from the National Second Soil Survey

this paper analyzed the variation of topsoil organic carbon(SOC) content in cropland and non-cropland

and the difference of SOC content in cropland and non-cropland

paddy fields and upland field among 6 regions.At the same time

the change of topsoil SOC storage led by cultivation was estimated based on the data of SOC content in non-cropland and cropland area.The results indicated that the variation of SOC content in cropland was less than that in non-cropland

and that in paddy field was less than in upland field;secondly

the SOC content in cropland was less than that in non-cropland which decreased 51.5% in average

but that in paddy field was more than in upland field;thirdly

the loss of SOC pool led by the agriculture cultivation was 4.3 Pg

which including the decreasing of paddy field and upland field was 0.67 and 3.63 Pg respectively.At last

this paper analyzed the spatial distribution of the SOC pool loss

and discussed the reason of the most decreasing degree of SOC storage in Northeast and Northern China

which was the much cultivation of soil like black soil

chernozems

and dark brown soil in grassland and wetland

and the irrational agricultural field management.