【Objective】 Converting agricultural straw into biochar and then returning it to the field has received widespread attention at home 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 soil column experiments of rice-wheat paddy-upland rotation and millet-wheat upland-upland rotation established in June 2011, the changes in the quantity and chemical composition of organic carbon in paddy soils (QP and TP) and upland soils (QU and TU) developed from Quaternary red clay and Tertiary red sandstone soils under long-term straw biochar application(BC0, 0 t·hm^-2 per season; BC11.3, 11.3 t·hm^-2 per season) were analyzed. We used ¹³C solid-state NMR to clarify the differences in carbon sequestration effect of biochar application on different acidic red soils. 【Result】 The results showed that: (1) soil texture, land use type, and their interaction significantly affected soil organic carbon density under biochar treatment. Compared with BC0, under the same land use pattern, 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 than upland soils after 11 years of BC11.3 treatment. (2) Under the same land use pattern, there was no significant difference in the contents of each functional group of soil organic carbon with different textures. The change in the utilization pattern of paddy and upland significantly affected soil organic carbon stability. The proportions of alkyl carbon and o-alkyl carbon in paddy soil were higher than those in dryland soil, and the proportion of aromatic carbon was lower than that in upland soil. Also, the stability of retained organic carbon in upland soil was higher. 【Conclusion】 We observed that the organic carbon sequestration potential of partial clay soil is higher than that of sandy soil after long-term straw carbonization and returning to the field in the acidic red soil area of South China, but there was no difference in long-term stability. Organic carbon sequestration in paddy soils was greater than in upland, but the stability of soil organic carbon was lower than in upland soils.