Fenfluramine can inhibit appetite, so many merchants illegally added it to food for sale. After eating fenfluramine, it can cause liver dysfunction, valvular heart disease, primary pulmonary hypertension, and other diseases that seriously affect health. Therefore, studying fenfluramine molecules' structure, spectrum, and molecular excitation is of great practical significance. This work used the density functional theory (DFT) method with theB3LYP functional and 6-311++G (2d, 2p) basis set for structural optimization. Furthermore, a series of studies were done on the structure, frontier orbits, Raman spectra, electrostatic potential, and UV spectra of the fenfluramine molecule. The basic structure information was obtained. The highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) were both alpha + beta orbits. The energy of HOMO, LUMO, and their energy gap was -6.25, -1.22 and 5.03 eV, respectively. There were two strong peaks at 756.5 and 1 003.5 cm^-1 in the experimental Raman spectrum. The strong peak at 756.5 cm^-1 was the symmetric deformation vibration of CF₃ and the asymmetric deformation vibration of C═C on the benzene ring. The strong peak at 1 003. 5 cm^-1 was the symmetrical deformation vibration of C═C on the benzene ring, the characteristic band of meta-disubstituted benzene. The linear fitting equation of experimental Raman spectra and calculated Raman spectra is y=0.988x+10.328, R²=0.999, showing good consistency. This work alsodiscussed the electrostatic potential and excited state properties of fenfluramine. The fenfluramine molecule contained 17 electrostatic potential energy maximum points and 12 electrostatic potential energy minimum points. The surface area distribution of electrostatic potential energy in the range of -0.01～0.025 a.u. was relatively uniform. The UV spectra were mainly determined by the first, second, and third excited states, and the contribution of the second excited state was as high as 82.516%. The electron excitation characteristics were studied by using hole-electron analysis. It could be found that S0→S1 and S0→S2 were attributed to the n-pi^* charge-transfer excitation in the direction from the amino group to a benzene ring. S0→S3 was attributed to the superposition of the n-pi^* charge-transfer excitation in the direction from amino group to benzene ring, and the n-σ^* local excitation between ammonio to carbon chain nearby. These basic theoretical calculations provide a theoretical basis for not only the detection of illegally added fenfluramine in food but also the study of its derivatives.