Catechin-black rice anthocyanin complex was chemically synthesized by black rice anthocyanin using acetaldehyde-mediated. The reaction mechanism of catechin - black rice anthocyanin complex was determined by infrared spectrum and thermodynamic parameters. The results showed that the catechin-black rice anthocyanin complex had a wide and strong absorption peak of —OH stretching vibration region at 3 207.90 and 3 217.90 cm^-1, and appeared the benzene ring skeleton vibration absorption peak at C=C stretching vibration region around 1 604.92 and 1 605.65 cm^-1. The infrared absorption peaks appeared at 1 278.01, 1 138.34 and 1 018.19 cm^-1 in the 1 300~1 000 cm^-1 C=O telescopic vibration region. It can be concluded the catechin-black rice anthocyanin complex and black rice anthocyanin had basically same structure framework with the main structure of aromatic ring structure —OH, C=C and C=O substituted groups. Compared with black rice anthocyanin, of catechin-black rice anthocyanin complex had the absorption peak not only at 1 604.92 and 1 493.59 cm^-1, but also at 1 454.78, 1 233.98 and 817.56 cm^-1. Based on absorption peak assignment, it was found that the absorption peak at 1 454.78 cm^-1 belonged to —CH₃ antisymmetric deformation or —CH₂ deformation vibration band, which proved the existence of “ethyl bridge” in catechin-black rice anthocyanin complex. It was confirmed that there was condensation reaction between catechin and black rice anthocyanin. The appearance of absorption peaks of 817.56 and 1 233.98 cm^-1 indicated that the plane valence bonds of some groups bent after the condensation reaction between catechin and black rice anthocyanin, which increased the polarity of C=O bond. In addition, the results of thermodynamic parameters showed that the condensation reaction between catechin and black rice anthocyanin was endothermic and non-spontaneous, and the structure of catechin-the black beige complex was stable.