Abstract: Taking cotton straw as the test material and fourier transform infrared spectroscopy（FTIR） analysis method, with saline alkali wasteland as the control（0 year）,the basic physicochemical properties and organic carbon chemical structure of cotton field soil after 5,10,15 years, and 20 years of cotton straw return were set, the change trend of soil organic carbon（SOC） structure under the condition of cotton stalk returning to field was studied, in order to provide reference for studying soil organic carbon sequestration under the addition of exogenous organic matter.The results showed that long-term cotton straw returning significantly increased soil organic carbon content, while the soil moisture content in the 20-40 cm soil layer was also increased, reducing soil conductivity.With the extension of the cotton straw returning period, the soil organic carbon lipid group characteristics showed a trend of first increasing and then decreasing, with the highest value after returning for 15 years.After returning straw to the field for 20 years, the soil organic carbon aromaticity increased, and the organic carbon structure changed from simple to complex.Overall, long-term return of cotton stalks to the field simplifies the chemical structure of soil organic carbon.