Diffusion characteristics of gold clusters (consisting of 38, 79, 140, or 586 atoms) on two types of defective graphite surfaces, one with a one-layer deep hole and the other with a one-layer high step edge, are studied with the use of molecular dynamics simulations. The effects of the defects on the energetics of the cluster and on the diffusive trajectories are investigated. The simulations guide formulation of a simple analytic model that is demonstrated to provide an appropriate description of the energy and of the forces acting on a cluster diffusing on a graphite surface in the presence of defects.