Peptides are important biological molecules. Ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy are important methods for studying the fine structure of biomolecules. The structures and molecular frontier orbital of Growth hormone-releasing peptide (GHRP-6) and Oxytocin were calculated by density functional theory (DFT/RI). Based on time-dependent density functional theory (TDDFT), TDA and other parameter approximations are introduced to establish theoretical models for calculating the UV-Vis and fluorescence spectra of peptides. For GHRP-6, UV spectrum peak is λ_cal.=282 nm (λ_Exp.=279 nm, Δλ=3 nm, E_r<2%), and fluorescence spectrum peak is λ_cal.=368 nm (λ_Exp.=360 nm, Δλ=8 nm, E_r<3%). For Oxytocin, UV spectrum peak is λ_cal.=269 nm (λ_Exp.=275 nm, Δλ=6 nm, E_r<3%), and fluorescence spectrum peak is λ_cal.=305 nm (λ_Exp.=312 nm, Δλ=7 nm, E_r<3%). The fluorescence emission wavelength produced by GHRP-6 is similar to the fluorescence wavelength range produced by tryptophan, indicating that the main contribution of GHRP-6 fluorescence is the π^*→π orbital transition on the tryptophan residue, Oxytocin fluorescence peak position is similar to the fluorescence wavelength range produced by tyrosine. The main contribution of Oxytocin’s fluorescence is the π^*→π orbital transition on tyrosine residues. Calculation results obtain via theoretical models are in good agreement with the experimental. It shows that the models are feasible to accurately calculate the UV Vis absorption spectra and fluorescence spectra of polypeptides, providing reliable theoretical guidance for experiments.