The dissociative adsorption of H-2 On both perfect and imperfect Cu(100) surfaces is studied by using a mixed quantum-classical method. The six-dimensional potential energy surface (PES) is obtained via a simplified embedded-atom method (EAM). The effects of the surface vacancy and surface impurity (here a substitutional Ni atom is considered) on the dissociation of H-2 are taken into account. The variation of activation barriers for H-2 dissociation near a surface defect with different pathways and different molecular orientations is investigated. Dissociation probability P-d is computed as a function of incident translational energy E(i) for different vibrational and rotational states. It is found that the presence of both vacancy and impurity atom Ni enhances the dissociation of hydrogen molecule on Cu(100) surface. Meanwhile, the general variation trend of P-d with the rotational quantum number J is unchanged, i.e., P-d first decreases and then increases as J is increased.