For the synthesis of two-photon excited probes, fluorophores based on excited-state intramolecular proton transfer (ESIPT) become critical. The ESIPT process of 2-butyl-4-hydroxyisoindoline-1, 3-dione is analyzed in this paper by DFT and TDDFT methods. We choose three non-protonic solvents to study their solvation effect. By examining infrared vibration spectrum data, optimized geometric structures and reduced density gradient, the hydrogen bond strengthened after photoexcitation and increased gradually with the decrease of solvent polarity. The proton transfer in the excited state is a low-barrier ultrafast process. The observed fluorescence peak in the experiment is derived from the emission of the tautomer form. Compared with the reaction barriers on the potential energy curves for different non-protonic solvents, a weaker polar solvent is more favorable to the ESIPT process.