Density functional theory(DFT)and time-dependent density functional theory(TDDFT)methods are used to investi-gate the influences of intramolecular and intermolecular hydrogen bonding on excited-state intramolecular proton transfer(ESIPT)for the 4-N,N0-(diethylamino)-2-hydroxybenzaldehyde(DEAHB).The structures of DEAHB and its hydrogen-bonded complex in the ground-state and the excited-state are optimized.In addition,the detailed descriptions of frontier molecular orbitals of the DEAHB monomer and DEAHB-DMSO complex are presented.Moreover,the transition density matrix is worked out to gain deeper insight into the orbitals change.It is hoped that the present work not only elaborates different influence mechanisms between intramolecular and intermolecular hydrogen bonding interactions on the ESIPT process for DEAHB,but also may be helpful to design and develop new materials and applications involved DEAHB systems in the future.