In this study, we optimized the range-separation parameter (μ) of LC-BLYP, a long-range corrected density functional theory (LC-DFT) method, using various fitting methods to accurately predict the absorption spectra of molecules with charge transfer (CT) characteristics. The μ value optimized in the gas-phase based on Koopmans' theorem exhibited a blue-shift compared to the experimental absorption peaks, whereas the μ value optimized in the solvent environment showed a significant red-shift. In contrast, the μ value adjusted to match the experimental data reproduced well the peak positions and intensities of the absorption spectra, and successfully predicted the energy differences of the maximum absorption peaks in C-DNP and C-OH. Furthermore, the HOMO and LUMO of C-DNP maintained a consistent shape for all μ values, and the electron transition from HOMO to LUMO clearly demonstrated intramolecular charge transfer (ICT) from the coumarin (C) moiety to the DNP group.