Abstract Chloride-induced rebar corrosion is a common degradation process for concrete infrastructures, which is a practical concern in coastal areas. It is essential to study the chloride diffusivity behavior in concrete. Considering the concrete heterogeneity, a meso-scopic numerical model based on the finite-element method is developed for the simulation of chloride diffusivity. Concrete is regarded as a heterogeneous material consisting of three components, i.e., aggregate, mortar matrix and the Interfacial Transition Zones (ITZs). A random aggregate structure of concrete is built, in which the mortar matrix is considered homogeneous. The aggregate phase is set as impermeable, and the chloride diffusion is assumed to take place only in the mortar matrix and the ITZs. The diffusion properties of the mortar matrix are determined based on the water/cement ratio, degree of hydration and porosity gradients away from aggregate particles. The transport equations are solved using the finite-element method, in which the three components are meshed separately and the continuity in fluxes at interfaces between them is applied. The present numerical model is validated against the available test data from the literature and compared with analytical results for ideal cases. Using the finite-element simulation method, a parametric study has been undertaken to understand the influences of the meso-structural parameters, including aggregate distribution, aggregate shape, diffusivity properties of the ITZ, water/cement ratio and aggregate content. The simulation results indicate that both aggregate distribution and aggregate shape have a negligible influence on chloride ingress in concrete, the diffusion properties of the ITZ and aggregate content have a significant impact, and the water/cement ratio has a marked effect.