The lipophilic azo dye Sudan Red Ⅲ molecule enhances flavor or makes food bright and attractive. After eating, it has noticeable toxic effects on the liver and kidney organs of the human body and seriously affects human health. The toxicity of Sudan red molecule is closely related to its molecular geometry and electronic structure, which has important guiding significance for studying its structure and electronic excitation. In this work, we aimed to systematically investigate the molecular structure, infrared and Raman spectra, and ultraviolet spectra of Sudan Red Ⅲ by using the density functional theory (DFT) method in conjunction with the def2-TZVP basis set. The excitation properties of Sudan Red Ⅲ were also studied in detail by the hole-electron analysis method. The results show that the infrared and Raman spectra calculated for Sudan Red Ⅲ using the PBE0 and B3LYP exchange-correlation functional agree with the experimental data. Using the time-dependent B3LYP (TD-B3LYP) method with the def2-TZVP basis set, The UV-visible absorption peaks of Sudan Red Ⅲ show 228, 353, and 490 nm, which are in good agreement with the experiments. It can be found that they are through the transition of the ground state electrons to the second excited state, the sixth excited state, and the 30th excited state. The electron excitation characteristics are studied by using hole-electron analysis. It can be found that S0→S2 is attributed to the superposition of the n—π* charge-transfer excitation in the direction from oxygen and nitrogen atoms to the naphthalene and benzene ring, and the π—π* local excitation between intra-ring naphthalene and benzene rings. The superposition of the n—π* charge-transfer excitation from oxygen and nitrogen atoms to naphthalene and benzene ring and the π—π* local excitation between intra-ring naphthalene and benzene rings are excited by S0→S6. The electronic transition of S0→S2 and S0→S6 from the ground state to the excited state belongs charge transfer excitation, where the charge transfer excitation effect is dominant. S0→S30 is attributed to the superposition of local excitation and charge-transfer excitation, where the local excitation effect is dominant. They contributed π—π* local excitation between intra-ring naphthalene rings, and the superposition of n—π* in the direction from oxygen and nitrogen atoms to naphthalene and benzene ring and π—π* charge-transfer excitation between intra-ring naphthalene rings. Furthermore, we draw heatmaps of the contribution of molecular fragments to holes and electrons. The electron mentioned above excitation transfer was further confirmed by heat map analysis. The spectrum and electron excitation of Sudan Red Ⅲ were investigated systematically, which can provide a theoretical reference for experimental detection of Sudan Red Ⅲ in food.