【Objective】Fertilization has become increasingly common to increase soil organic matter (SOM) content and improve soil fertility. Research suggests that fertilization promotes production of humic acids (HAs), one of the most important component of SOM.However little is known about the quantitative effects of fertilization on structural characteristics of HAs. Based on the long-term field fertilization experiment in Fegnqiu of Henan, effects of application of organic manure (OM), chemical fertilizer (NPK) and nothing (CK) on structure of HAs in fluvo-aquic soil were assessed. 【Method】Soil samples were collected from the surface soil layers of three treatment plots, i.e. OM, NPK and CK, of a long-term winter wheat (Triticumaestivum L.)-summer maize (Zea mays L.) rotation experiment in Fengqiu, China.HAs were exhaustively extracted from the soil samples with a combined 0.1 mol L^-1NaOH and 0.1 mol L^-1 Na₄P₂O₇ solutionand obtained through precipitation after acidification with 6 mol L^-1HCl. HF:HCl (1%:1%) solution was then used to purify the HAs obtained. In the end, the purified HAs were characterized with advanced solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy coupled with elemental analysis and isotopic analysis (δ¹³C). The NMR techniques included multiple cross-polarization/magic angle spinning (multiCP/MAS), dipolar-dephasing (DD), chemical-shift-anisotropy (CSA) filter and spectral editing of immobile CH₂ and CH. 【Result】Results show that long-term fertilization changed the element compositions, δ₁₃C ratios and carbon functional groups of HAs, particularly significant in Treatment OM, and increased saturation degree, oxidation degree and polarity of HAs, but decreased condensation degree of HAs. The decrease of HAs in δ₁₃C valuesindicated incorporation of new organic carbon into HAs. Advanced NMR techniques revealed that HAsin fluvo-aquic soil were composed predominantly of aliphatic compounds with alkyl being the highest in percentage (24.1% ~ 26.3%).OCH₃ and NCH signals both resonated around δ64 ~ 44, while the latter was prominent in proportion. Besides, the proportion of nonprotonated carbon was very low in anomeric and O-alkyl. Among the aromatics of HAs, they were dominated with protonated carbon inδ142 ~ 113, while only a little aromatic carbon existed in δ113 ~ 93, which cannot be detected with the routine cross-polarization/magic angle spinning (CP/MAS) NMR. It was also found that long-term fertilization reduced the percentages of COO/N-C=O and aromatic carbon of δ142 ~ 113, but increased the percentages of O-alkyl and OCH₃. Moreover, application of organic manure also increased the proportions of aromatic C-O and NCH, but decreased that of alkyl.【Conclusion】In conclusion, all the findings in this study indicate that HA structure tends to be less hydrophobic with decreasing degree of decomposition. The application of either OM or NPK increases the content of carbohydrates in HAs. The application of OM also increases the contents of lignin and peptides, but decreases the content of lipids. The study also suggests that the advanced NMR techniques could provide great insight into HA structure and mechanisms of HA formation relative to fertilization pattern.