AgNO3 colorimetric method was introduced to study the effect of cracks on diffusion of chloride in concrete, taking the relationship between the load crack width and crack depth into account. Through drilling powders, the chloride content in concrete was measured and the influence of crack width or crack depth on the chloride diffusion process was studied. The results indicate that cracks accelerate the diffusion of chloride in concrete. The chloride diffusion coefficient increases with the increase of crack width. The crack depth also has certain influence on the chloride diffusion process. Based on test results, an exponential relation between the crack width(crack depth) and the chloride diffusion coefficient is established.