Abstract: In this study, three dimensional excitation-emission matrix spectra (3DEEMs) was combined with parallel factor analysis (PARAFAC) model, we analyzed the spatial and temporal variation and composition of dissolved organic matter (DOM) in the water near the mouth of the Yangtze River Estuary from August 2020 to April 2021. The results show that: In the study area, dissolved organic carbon (DOC) concentration was the highest in autumn (2.76 mg/L), followed by summer (2.56 mg/L), and was lower in spring (1.96 mg/L) and winter (2.11 mg/L), with no significant difference between them; The regional distribution of DOC concentration was characterized asthe southern branch Beigang (3.20 mg/L) > the northern branch (2.21 mg/L) > the northern branch Beisha (1.82 mg/L). DOM in the water can be divided into four components, namely aromatic amino acid component C1, terrestrial and marine humus component C2, tryptophan-like component C3 and humus-like component C4 of marine origin C4, Components C1、C2 and C3 have homology, among which C1 and C2 occupy the dominant position, C3 takes the second place, and C4 occupies the smallest proportion; The proportions of C1 and C4 increased with the increase of offshore distance, while C3 decreased; The proportion of component C1 was the largest in winter and the smallest in summer, and the proportion of component C3 and C1 was opposite. The analysis results of fluorescence characteristic parameters showed that most of the DOM in the water was the joint action of terrigenous input and aquatic biological activities, and the authigenic characteristics were significant, while the humification characteristics were weak. To some extent, it indicated that thewater body in the study area was highly active and the water quality was good.