Density functional theory (DFT) at B3PW91/6-31G** level was employed to investigate the structure and vibrational frequencies of reactants, intermediates, transition states and products in the chemiluminescence reaction of luminal-DMSO-NaOH system. Reaction enthalpies and the Gibbs free energies were calculated at B3PW91/6-311＋G(3df,2p) level with thermal corrections from the scaled frequencies of B3PW91/6-31G**. Electronic excitation states and energies of the key luminescence species AP^2－ were analysed by time-dependent DFT method at B3PW91/6-311＋G(3df,2p) level. This study, in the point of view of quantum theory, supported the chemiluminescence mechanisms of the reactions LH₂(¹A)＋OH^－→LH₂•OH^－(¹A)→LH^－(¹A)→ (²A)→TS₁(³A)→LO₂^2－ (³A)→TS₂(³A)→AP^2－*(?³A)→AP^2－(X³A)＋hν. In the last step, the potential energy hypersurface of the excited triplets AP^2－*(?³A) may also cross-link with that of the singlets AP^2－*(?¹A) and lead to chemiluminescence of singlets transitions AP^2－* (?³A)→AP^2－*(?¹A)→AP^2－(a¹A)＋hν. Two peaks of intense emissions in the ranges of 400～460 and 500～530 nm of visible lights were found. This has largely supported (with respect to the complexity of solvent effects) the experimental chemiluminescence spectra of luminal-DMSO-NaOH system. It has also been found that luminol will be greatly stabilized by protonation and therefore, the activity of luminol is extremely low in acidic solutions and the chemiluminescence intensity is influenced by acidity of solutions.

Key words: luminol, DMSO, chemiluminescence, mechanism, DFT