In this paper, the lattice network model on mesoscale is established based on the random geometry meshing technique to investigate the chloride ingress into unsaturated concrete. Concrete is treated as a composite material with three phases, i.e., the coarse aggregates, the mortar, and the interface between them. The diffusivity for water and chloride in each phase of the mesoscopic structure of concrete is separately quantified by experimental data or through empirical assumption. The numerical predictions are compared with the available experimental measurements. The comparisons indicate that numerical predictions agree well with the test results.