Geostatistics combined with classic statistics was applied to analyze the spatial variability and reasonable sampling number of soil organic carbon at county scale in the gully and plain regions of the Loess Plateau. The results showed that: 1) The coefficient of variation was relatively small in the gully region, ranging from 0.176 to 0.200. The plain presented a larger coefficient of variation, ranging from 0.24 to 0.26. 2) Classic statistical analyses showed reasonable sampling number was 64 in the gully region and 110 in the plain region by the 5% accuracy and 95% confidence interval. 3) The two regions both presented strong spatial dependence and small range, being 2250 m and 900 m respectively. In Zhuanglang County, the SOC contents in the north were higher than those in the south, the SOC contents in the west were higher than those in the east part, and some high values were in patch forms. In Wugong County, the SOC contents in the southwestern and central parts were high, and the high values were more concentrative. Based on the spatial correlation of SOC and validation,we concluded that reasonable sampling number of SOC was about 903 and 1838 in the gully and plain region respectively. The study was important to reasonably evaluate the prediction accuracy about soil organic carbon storage in the Loess Plateau region.