In order to study the chloride transport process in real concrete, an electron probe technique was applied to establish a 3D mesoscopic numerical model of concrete by reconstructing the special aggregate distribution and pore structure. Taking the interfacial transition zone(ITZ) into consideration, the chloride transport in concrete was simulated based on Ficks second law. The model was verified through electron probe measurement. The research indicates that the outward and inward concave has impact on the density, outline and the chloride isolines of transfer direction. The irregular shape aggregate will enhance the tortuosity of transfer flux, while ITZ can provide a rapid transport path which will undoubtedly accelerate the chloride transfer.