Abstract: In order to further explore the specific effects of long-term addition of exogenous organic materials on soil inorganic carbon pool in farmland, this study carried out a study on the effects of different fertilization treatments on soil carbon pool distribution and related physicochemical properties based on a 16-year long-term positioning experiment in farmland in North China. Six treatments were set up, including control (CK), nitrogen fertilizer (N), chemical fertilizer (NPK), nitrogen fertilizer combined with organic fertilizer (MN), chemical fertilizer combined with organic fertilizer (MNPK), and chemical fertilizer combined with straw (SNPK). In this study, the effects of different fertilization treatments on soil organic carbon (SOC), inorganic carbon (SIC) content and other key soil physicochemical properties were analyzed in detail, and the mechanism of exogenous organic material addition on soil carbon pool change was discussed by principal component analysis. The results showed that the long-term addition of exogenous organic materials significantly increased SOC content in 0-20 cm soil layer. Compared with CK, MNPK increased SIC content by 7.0% in 0-60 soil layer, while SNPK decreased by 7.6%. In 50-60 cm soil layer, SNPK caused 27.9% loss of SIC. The decomposition of straw produces organic acids and CO₂, and promotes the mineralization of background SOC to produce CO₂, which leads to a significant decrease in soil pH, which may be the main reason for the significant loss of SIC in the deep layer of SNPK. The research results not only provide theoretical basis for revealing the transformation mechanism of soil carbon pool after the addition of foreign organic materials, but also have important significance for evaluating the key role of SIC in soil carbon storage.