Air pollution is a serious global health problem nowadays. So, it is an emergency to pay sufficient attention to treat and prevent the diseases caused by air pollution, especially respiratory disease and lung damage. Cladina rangiferina (L.) Nyl. is an edible lichen that has been used in medicinal diets to treat respiratory and other diseases for over 500 years. In this study, a water-soluble polysaccharide, CRWP-P, was obtained from C. rangiferina by hot-water extraction, freeze-thawing separation, and Fehling reagent purification. Structural analysis showed that CRWP-P is a linear α-(1 → 3),(1 → 4)-d-glucan without branches. Its Mw was determined to be 1.05 × 105 Da. Its (1,3)-α-d-glucopyranosyl: (1,4)-α-d-glucopyranosyl ratio is approximately 1:2. Antioxidant activity assay showed that C. rangiferina polysaccharides, especially CRWP-P, had appreciable DPPH radical-scavenging activity and reducing power. Notably, they could effectively decrease cell breakdown and ROS generation, inhibit lipid peroxidation, increase key antioxidase activity, and promote glutathione redox cycling in Pb2+-oxidative injured A549 alveolar epithelium cells. Overall, the results of this study indicated that C. rangiferina polysaccharides, especially CRWP-P, have the potential to be natural antioxidants for the treatment of lung oxidative damage induced by lead of air pollutants.