【Objective】 Converting agricultural straw into biochar and then returning it to the field has received widespread attention at domestic and abroad as a potential pathway for soil improvement and carbon sequestration and emission reduction in the southern acidic red soil area. 【Method】 Relying on the soil column experiments of rice-wheat (paddy-upland）rotation and millet-wheat (upland-upland) rotation established in June 2011, the organic carbon accumulation characteristics and changes in the organic carbon functional group structure of paddy soils (QP and TP) and upland soils (QU and TU) developed from Quaternary red clay and Tertiary red sandstone soils were observed under long-term straw biochar application (BC0, 0 t·ha-1 per season; BC11.3, 11.3 t·ha-1 per season). The relationship between soil organic carbon quantity, structure, stability indicators and soil properties was analyzed, in order to clarify the differences in carbon sequestration effect of biochar application on different acid red soils. 【Result】 The results showed that soil texture, land use type and their interaction significantly affected soil organic carbon density under biochar treatment. Compared with BC0, the increase in soil organic carbon density from 0-20cm was higher in partial clayey soils (QP, 25.22 kg·m-2; QU, 8.07 kg·m-2 ) than sandy soils (TP, 8.67 kg·m-2; TU, 7.58 kg·m-2 ), and higher in paddy soils (QP, TP) than upland soils (QU, TU) after 11 years of BC11.3 treatment. The results of 13C solid-state NMR showed that under the same farming conditions, there was no significant difference in the composition of organic carbon functional groups and stability indicators of soil with different textures. The ratio of alkyl carbon and o-alkyl carbon in paddy soil is higher than that in dryland soil, and the ratio of aromatic carbon, hydrophobicity index and aromaticity are lower than that in dryland soil. pH, bulk density, field water capacity, and total porosity all significantly affected the soil organic carbon content and its stability indicators after biochar application. 【Conclusion】 The above results show that the organic carbon sequestration of partial clay soil is higher than that of sandy soil after long-term straw carbonization and returning to the field in the sour red soil area of South China, but there is no difference in long-term stability. The sequestration of organic carbon in paddy field is larger than that in upland, but upland is more conducive to the long-term stability of soil organic carbon. In this study, we investigated the mechanism of carbon sequestration effect difference between different soils from soil organic carbon and its structural characteristics, and provided scientific basis for the rational use of straw biochar resources.