A three-dimensional random aggregate model was established by numerical simulation to analyze the effects of different coarse aggregate shapes， contents， particle size and multiple particle size combinations on the chloride diffusion coefficient in concrete. The results were verified by the rapid chloride migration test. The results show that the smaller the shape parameter of the coarse aggregate in the same volume， the more signifacant the hindrance of chloride diffusion. Within a range of certain concentration， the chloride diffusion coefficient decreases gradually with increasing coarse aggregate content. The chloride diffusion coefficient decreases with the increasing of the coarse aggregate particle size for a certain volume fraction， and increases with the increasing of the number of particle sizes combined into coarse aggregates for the same volume fraction.