In order to clarify the changes in soil organic carbon components under different straw returning methods，this study was based on a 7-year long-term positioning experiment of straw returning. Three-dimensional fluorescence spectroscopy technology was used to analyze the soil organic carbon content，fulvic acid content，and structural characteristics under CK(no straw returning)，FG(straw covering returning)，FM(straw burying returning)and FH(straw mixed returning)treatments. The results showed that:(1)Different straw returning methods were more conducive to the accumulation of soil organic carbon and fulvic acid content in the surface layer(0-10 cm). Among them，straw covering returning treatment was the best，followed by straw burying returning treatment. Compared with CK treatment，the organic carbon and fulvic acid content increased by 16.86%，16.80% and 67.30%，57.21%，respectively. FG and FH treatments reduced soil organic carbon content by 7.67% and 3.68% in the 30-40 cm soil layer，respectively. FG treatment reduced the content of fulvic acid in the sub surface layer(20-30 and 30-40 cm)，while FH treatment reduced the content of fulvic acid in the soil layer of 30-40 cm by 25.19%.(2)The sources of fulvic acid in soil humus were influenced by both endogenous and exogenous sources. FM treatment showed an increase in FI，BIX and HIX in the four soil layers compared to CK. This indicated that FM treatment had a higher degree of soil humification and better stability in different soil layers.(3)The three-dimensional fluorescence spectrum and fluorescence region integration indicated that FM，FG and FH treatments all increased humic acid substances，resulting in a higher degree of humification and a more complex structure. Three fluorescent components were identified in this experimental area. Among them，Component 1(Excitation/Emission=330/410)and Component 3(Excitation/Emission=270，370/460)were both humic acid substances，mainly derived from organic matter produced by the decomposition of higher plants；Component 2(Excitation/Emission=230，260/415)was a fulvic acid substance；The higher the relative content of Component 3，the higher the degree of soil humification. Compared with CK，the relative content of Component 3 in FM treatment increased by 3.8%-15.44% in the four soil layers. In summary，burying and returning straw to the field was the best way to increase soil humification and enhance soil fertility.