In view of density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, we investigated the influence of solvent polarity on the excited state intramolecular proton transfer (ESIPT) behavior and spectral properties of 2‑butyl‑4-hydroxyisoindoline-1,3‑dione (BHD). In this work, five different solvents were selected: acetonitrile (MeCN), dichloromethane (DCM), tetrahydrofuran (THF), Benzene and n-Heptane. The experimental absorption and fluorescence wavelengths in MeCN were duplicated theoretically, which proved the reliability of the chosen method. The ESIPT process was easy to occur due to the enhanced intramolecular hydrogen bond (H-bond) in the excited state (S1), which has been confirmed by a series of results related to the H-bond. When the dielectric constant of solvent reduces, the influence of solvent polarity on spectral characteristics and ESIPT behavior included the following aspects: the ground state intramolecular H-bond strength and HOMO-LUMO energy gap became stronger and larger, respectively, while the corresponding parameters of excited state became weaker and smaller, respectively; the forward and reverse ESIPT barrier increased and decreased, respectively. Especially, the H-bond strength of S1 state and the red-shift value of O1H2 bond were linear with the dielectric constant of solvent.