As a Cenozoic antibody, chicken egg yolk immunoglobulin (IgY) has the characteristics of safety, stability and no drug residue. It has an inhibitory effect on a variety of pathogenic microorganisms. IgY is one of the ideal substitutes for antibiotics. However, it cannot be used on an extensive scale application to a certain extent because of its high production cost and low antibacterial activity caused by protease decomposition. Therefore, it is of great significance to improve its economic benefit and bioavailability using modification. In this study, catechin interacted with IgY to prepare its complex. It provides support for improving the antibacterial properties of IgY and preparing safer and more efficient antibacterial agents. The interaction mechanism between catechin and IgY was studied via UV-Vis, FS and FT-IR. The antibacterial properties of the IgY-catechin complex were studied by using IgY and a mixture of IgY and catechin as control. With the increase of catechin concentration, the UV-Vis absorption peak value of IgY gradually increased and showed a blue shift. The quenching type of IgY by catechins is mainly static quenching. The IgY and catechin combine to form a complex with a number of binding sites close to 1. The interaction types were van der Waals force and hydrogen bond. Compared with IgY, the content of β-folded and β-corner in the secondary structure of the IgY-catechin complex had no significant change, while the content of α-helix was increased and irregular convolution was decreased. It indicated that the conformation of protein was changed due to the introduction of catechin. Compared with IgY and a mixture of IgY and catechin, the antibacterial rate of IgY-catechin complex against Staphylococcus aureus was increased by 135.8% and 9.95% on average, respectively. When the concentration was greater than 0.05 mg·mL^-1, the antibacterial rate against Escherichia coli was increased by 15.74% and 13.27%, respectively. Catechins and IgY could form a complex, which showed better antibacterial properties than IgY and mixture of IgY and catechin. This study is helpful in understanding the effects of catechins on the structure and function of IgY. It can also provide theoretical support for preparing safer and more efficient antibiotic substitutes. In addition, this study can supply theoretical guidance for the property changes of IgY during food processing.