In order to study the law of chloride ion erosion in unsaturated concrete of concrete bridges on service, a multi-factor modified model of chlorine ion transport for saturated concrete was established based on the characteristics of moisture migration in dry-wet circulation process and the influence factors of chloride ion transmission.It derived the coupling equations of water-chlorine transport convection-diffusion under non-saturated conditions.By integrating the macroscopical numerical model of chloride ion erosion with the mesoscopic random concrete model, a random mesoscopic study method for non-saturated chloride ion-eroded concrete was presented,and it summarize the rules that chloride ion transport in unsaturated concrete. The results indicate that the concentration of chloride ion concentration around the aggregate was significant.Different from the surface of concrete ,the aggregates have a great influence on the size and position of the chloride ion concentration peak. The concentration increased in wetting process , and decreased in drying stage due to the combined effect of convection and diffusion for the interior area .The research results for non-saturated concrete chloride ion transport mechanism provides a reference.