Coastal saline soil is a special type of land use, which has a low content of organic matter and a high capacity of carbon sequestration. The study on the spatio-temporal variation of organic carbon in coastal saline soil has practical significance in understanding the transformation of soil carbon source and sink and regulating climate change. This study was carried out using geostatistics and geographical information system(GIS)technologies to explore the spatio- temporal variability of soil organic carbon content in different soil layers(0~5,5~10,10~20,20~30,30~40, 40~60,60~80,80~100,0~100cm)in Dongtai City since 4000 BC. We found 2.01~10.16 g· kg~(-1) in the study area,and that different variation(strong,moderate or constant)was determined by the variation coefficient. According to geo-statistical analysis,strong spatial correlation was found in different layers of organic carbon and the value of the nugget effect varied from 0.01~0.51. The results of the ordinary Kriging demonstrated that soil organic carbon in the West Dike varied from 5.75~16.87 g· kg~(-1),while the value in the East Dike varied from 1.12~4.70g· kg~(-1). The soil organic carbon of Dongtai showed an increasing trend from beach to inland in whole soil layers. However, along with the increase in soil depth,soil organic carbon showed a banded decreasing trend with local characteristics and patches. Soil organic carbon content has a close relationship with soil depth,reclamation and fixed number of years,and land use. The average annual change in soil organic carbon content was 0.0017 g· kg~(- 1) at the Millennium scale,0.0055g· kg~(- 1) at the centennial scale,and 0.0048g · kg~(- 1) at the ten- year scale. This study indicates that there is spatio- temporal variation of coastal soil organic carbon content,which decreased with reclamation time and soil depth.