Abstract: Humic substances have important influences on dissipation of pollutants in soil. According to Pallo classification method, the three fractions of fulvic acid (FA), humic acid (HA) and humin (HM) were separated from the sediment in the Wusong estuary coastal wetland. The optical property Δlog K, infrared spectra and elemental composition of the humic fractions were analyzed. The results indicated that the content of humic substances in the Wusong estuary coastal wetland was 3.20 g/kg, and FA and HM were 40% and 55% of the total humic substances, respectively. Moreover, the Δlog K value of FA was higher than HA’s, showing that the degree of evolution and aromatization of FA was low. The main functional groups of FA and HA were —CH₂, —CH₃, —COOH, C=O and —CH₂, —CH₃,—COOH, C=C, respectively. Humic substances in the Wusong estuary coastal wetland belonged to low degree of humification and aromatization. The aromatization degree of humic substances was gradually enhanced by FA

Key words: humic substance, sediment, wetland, Wusong estuary