In order to reveal the characteristics of soil organic carbon and its chemical structure after combined application of bentonite and straw，this study selected four treatments from a 3-year field positioning experiment in the dryland area of the Loess Plateau，including straw returning(S)，single application of bentonite(B)，bentonite with straw(H)，no application of bentonite and straw without returning(CK)，to study the effects of bentonite and straw combination on the organic carbon content，organic carbon chemical structure and enzyme activity of the root zone soil. The results showed that both bentonite and straw application increased the soil organic carbon content to varying degrees，with H treatment significantly increasing by 19.65%，compared to CK treatment. Compared with CK treatment，only H treatment significantly increased the relative content of alkyl carbon and alkoxy carbon，as well as the aliphatic carbon/aromatic carbon ratio，by 25.53%，18.00% and 50.98%，respectively；Only H treatment significantly reduced aromaticity by 30.93%. Compared with CK，each treatment increased the alkyl carbon/alkoxy carbon ratio，with an increase of 5.26%-17.54%，and the difference was not significant；Each treatment reduced the relative content of carboxyl carbon and aromatic carbon by 24.50%-38.19% and 1.29%-21.97%，respectively，with no significant difference. Compared with CK，the sucrase activity of S，B and H treatments was significantly increased by 12.63%-33.16%，β-glucosidase activity was significantly increased by 10.72%-45.56%，and manganese peroxidase activity was significantly increased by 25.10%-70.98%. Correlation analysis showed that soil sucrase，β-glucosidase and manganese peroxidase activities were positively correlated with organic carbon content，alkyl carbon content and alkyl carbon/alkoxy carbon ratio，but negatively correlated with carboxyl carbon and aromaticity. In summary，the combination application of bentonite and straw can increase soil organic carbon content，increase soil enzyme activity，increase active organic carbon content，activate soil organic carbon molecules，and promote good soil improvement in the arid areas of the Loess Plateau.