Abstract: Polyphenols and dietary fiber can form complexes through their interactions. In order to investigate the interaction mechanism between polyphenols and dietary fibers, and the structure and morphology of complexes formed by them, this paper selected epigallocatechin gallate and oat β-glucan as the raw materials for the preparation of the complexes and their structural characterization. The results indicated that the formation of the complex of EGCG and oat β-glucan was related to the concentration and pH of EGCG, EGCG and oat β-glucan could form a complex with a particle size of 1.7 μm and a relatively uniform particle size (dispersion coefficient 0.38) in an aqueous solution with a mass ratio of 0.8:1 and pH5. Through transmission electron microscopy, the formation of regular spherical particles between EGCG and BG were clearly observed. Isothermal Titration Calorimetry (ITC) measurement was used to characterize the EGCG-BG complex. The binding mechanism at 25 °C clearly provided that the binding between EGCG and BG were mainly non-covalent interaction (such as hydrogen bonding and hydrophobic interaction). The above experimental results could indicate that EGCG and BG could spontaneously form a complex through non-covalent interactions. In summary, the findings of this study would provide a theoretical reference and research basis for the use of different polyphenol-oat β-glucan complexes as functional food ingredients or as bioactive materials.