More than 2000 soil samples obtained from the second soil census in China in the year 1998 were applied to analyse the correlations of soil organic carbon storage (SOC) and climatic factors, including annual mean temperature (T), and sum of precipitation (P). The results show that: (1) the correlations are quite different in different temperature zones. In the area where T ≤10 oC, the correlation between SOC and temperature has the strongest negative correlation. In the area where 10 oC 20 oC, the correlation between SOC and temperature and precipitation is inadequate. (2) Due to the strong positive correlation between temperature and precipitation in China, the partial correlation method is thus better than Pearson correlation method. (3) The correlation between SOC and temperature and precipitation in cultured soil is weaker than that of non-cultured soil, which could attribute to human activities. (4) 26 pairs of soil samples, each pair coming from the same place which has the same soil properties and the same climatic condition, and consisting of one sample in cultured soil and the other in non-cultured soil, are used to analyse the difference of soil organic carbon storage between cultured and non-cultured soil. The results show that the differences of SOC are significant in two types of soils, and as a whole there is certain SOC released to the atmosphere as forest or grassland is converted to cropland.