A model of impurity precipitate-dislocation generation, impurity atom-dislocation interaction and impurities rapid diffusion along grain boundaries has been used to explain the out-diffusion behaviour of implanted impurities and defect movement in the amorphous layers due to high dose ion implantation during reerystallization annealing. Taking the resultant stress effect of the dislocations in to account, the diffusion equation of impurities has been established. By using Pb+ ions with energy of 80 keV implanted in (111) silicon to the dose of 1016cm-2 as an example, a mathematical and physical treatment of the diffusion equation has been carried out. Thereby a method of deducing the apparent diffusion coefficient varying with time and the longitudinal profile of the force exerted by the resultant stress of dislocations on the impurities according to the experimental measurements has been proposed. The measured constant of interaction between dislocations and impurities, α, is α≈8.4×10-28dyn·cm3, and the time variation of the apparent diffusion coefficient D in a time interval can be expressed as a exponential function.