Abstract: In order to obtain an in-situ Fenton technique for effective oxidation of total petroleum hydrocarbons (TPH) in soils, the remediation of oil-contaminated soil by in-situ preparation of aggregated iron using fulvic acid (FA) was studied. The study focused on the effects of the aggregated iron groups and non-aggregated iron groups on the oxidation of the two types of oil-contaminated soils (S1, S2) with different textures and soil organic matter (SOM), as well as the mechanism of efficient in-situ oxidation of TPH in the aggregated iron groups. The results showed that: (1) In oil-contaminated S1 and S2 soils (the initial concent of TPH was 16,074.33 mg/kg and 14,528.17 mg/kg in S1 and S2 soils, respectively), the TPH oxidation level was as high as 7,550.32 mg/kg (S1) and 8,747.78 mg/kg (S2) in the aggregated iron group, which were higher than the corresponding values in the non-aggregated iron group Ⅰ (6,364.43 mg/kg, 5,730.73 mg/kg). It indicated that the aggregated iron group could remove TPH efficiently from soils. (2) In the S1 and S2 soils, the oxidation rates of medium-chain alkanes (C₁₉-C₂₄) were up to 20% and 22%, and long-chain (C₂₅-C₃₀) alkanes were 23% and 20% in the aggregated iron group, which were higher than the oxidation rates of non-aggregated iron group Ⅰ in S1 soil (17%, 18%) and S2 soil (19%, 12%), respectively. (3) Electron paramagnetic resonance (EPR) technology showed that the intensity of hydroxyl radicals (·OH) in the aggregated iron group (S1, 36.61 a.u; S2, 16.06 a.u.) was higher than the corresponding indicators in the non-aggregated iron group Ⅰ (S1, 27.78 a.u.; S2, 7.11 a.u.), and the hydroxyl radical durations (S1, 50 h; S2, 55 h) were also higher than the corresponding indexes in the non-aggregated iron group Ⅰ (S1, 45 h; S2, 40 h). (4) The high contents of FeOOH (S1, 503.52; S2, 850.01) and α-FeOOH (S1, 399.40; S2, 769.62) measured by XPS increased the instantaneous strength and yield of ·OH in the aggregated iron group. The 3DEEM results confirmed that the standard volume of the fluorescence region of fulvic acid in the aggregated iron group (S1, 1,554,047.24 au·nm²; S2, 1,110,373.00 au·nm²) was significantly higher than the corresponding values in the non-aggregated iron group (S1, 1,100,706.21 au·nm²; S2, 716,069.98 au·nm²), indicating that high FA content is beneficial for the aggregation of FeOOH and α-FeOOH in soils. Our study indicated that the aggregated iron group effectively catalyzed the removal of TPH from soils by H₂O₂, providing an economical and effective method for in-situ chemical oxidation remediation of oil-contaminated soil.