Based on the revised Fick's second law, a chloride diffusion model was established for bonded strengthened concrete. The influence of bonded reinforcement was considered as change of boundary conditions. This model could be applied to predict chloride diffusion in both non-strengthened and strengthen concrete. Numerical simulation of chloride diffusion in a reinforced concrete beam strengthened by externally bonding was carried out by ABAQUS, MATLAB PDE tool, MATLAB programming. Comparison of chloride diffusion in strengthened and non-strengthened specimens was conducted. The simulation results showed the service life of RC specimens could be extended by bonding externally.