<jats:p> Chloride penetration is one of the main causes for the failure of reinforced concrete structures, especially in undersea tunnels, which is also accompanied by stress and seepage water-induced calcium leaching. In this paper, the chloride penetration resistances of concrete under the single and dual effects of stress and calcium leaching were investigated, and the microscopic mechanism was explained by Scanning Electron Microscopy (SEM) and X-ray diffraction analysis (XRD). The results show that the chloride diffusion depth and chloride content linearly increase with the stress level in the tensile zone, while linearly decrease in the compressive zone, and the change is more obvious in the tensile zone. At stress levels of 15%, 30%, and 45%, the diffusion depth in the tensile zone increases by 11.4%, 36.6%, and 43.5%, respectively, and the increased ratios of chloride content are 1.2%, 11.2%, and 19.4%. There is no significant synergistic effect between stress and calcium leaching on chloride diffusion depth, but it is obvious on chloride content, especially when the tensile stress level is below 15% and the compressive stress level is above 30%, for which the differences caused by considering the synergistic effect or not are approximately 6% and 15%, respectively. </jats:p>