Seven models with different structures of bound states are constructed by using several model potentials.Time-dependent Schrdinger equation is solved with pseudospectrum-split operator method to get the power spectra of seven models.The component of transactions referring to bound states is extracted to study the role of bound states in high-order harmonic generation.The results show that continuum-ground transaction plays dominant role in harmonic generation

whereas continuum-bound transactions

bound-bound transactions and resonance among bound states could enhance the intensities of harmonics in low-frequency region.In addition

the existence of bound states could add to the possibilities of continuum-ground transactions and then enhance the intensities of harmonics in plateau region.