Based on the classical stress level-fatigue life equation, a mathematical expression for chloride ion diffusion coefficient was proposed with the number of freeze-thaw cycles as independent variable. Furthermore, a three-dimensional mesoscopic numerical model of chloride ion transport in concrete under freeze-thaw cycles was established to investigate the effects of freeze-thaw cycles, mesoscopic structural characteristics of concrete, and bonding effects on chloride ion transport behavior. The results show that the freeze thaw cycle can promote chloride ion diffusion, and this promotion effect is significant when the number of freeze thaw cycles approaches the limit number of freeze thaw cycles. Furthermore, the mechanism of interfacial transition zone promoting chloride ion diffusion is revealed by simulating the diffusion trajectory of chloride ion in concrete meso-structure. Finally, through the simulation of the long-term diffusion performance of chloride ions, it is found that there is a saturated area of bound chloride ion near the ingress surface. And in the saturated area of bound chloride, the concrete loses the curing ability of free chloride and promotes chloride ion diffusion.