Abstract: Two types of models, displacement input model and uniform acceleration input model, for structural response calculation subjected to earthquake ground motions, are reviewed and discussed. It is found that the omitted damping terms in the two models are different, which may have significant influence on structural responses. It is recommended that displacement input model, rather than uniform acceleration input model, to be adopted in comparing seismic responses caused by consistent excitations with those caused by multi-support excitations, to avoid the influence of the difference in omitted damping terms. Moreover, it is pointed out, contrary to the current viewpoints, modal superposition method is not applicable to the displacement input model.