The effects of NaCl stress on ion balance and physiological and biochemical characteristics of Quercus dentata seedlings were tested to provide reference for understanding the salt tolerance mechanism and the application in landscape architecture. One year old seedlings of Q. dentata were used as plant materials, and were treated with 100 mmol/L, 200 mmol/L, and 300 mmol/L NaCl solutions for 30 days through Irrigation. The changes of ion contents and physiological and biochemical indexes were measured at different time. The results showed that with the increase of NaCl concentration and the prolongation of treatment time, the indexes of seedlings showed the following rules: (1) a large amount of Na⁺ was accumulated in roots, stems, and leaves, which caused ion toxicity, leading to leaf damage. And the Na⁺ contents of roots were significantly higher than that of aboveground parts, which was helpful to reduce the damage of aboveground parts; (2) the K⁺ contents of each part decreased, and in the roots the decreased degree was more significant than that in stems and leaves. This resulted in significant addition of Na⁺/K⁺; (3) Ca²⁺ transported from roots to the aboveground parts, and the contents of Ca²⁺ in leaves increased significantly, which helped to establish a new ion homeostasis; (4) The Mg²⁺ contents presented decreased trend on the whole; (5) the water content of leaves decreased gradually, and the content of malondialdehyde and relative conductivity increased gradually. And the change was more significant under severe stress; (6) Under mild salt stress, the activities of peroxidase (POD) did not showed obvious change, and the activities of catalase (CAT) and superoxide dismutase (SOD) increased gradually. Tut the activities of three enzymes decreased under severe stress; (7) The contents of proline and soluble sugar accumulated in a small amount to help regulate osmotic balance. In sum, Q. dentata seedlings can improve salt tolerance by regulating ion balance, enhancing antioxidant enzyme activity, and accumulating osmotic regulators. The Q. dentata seedlings can resist NaCl stress below 200 mmol/L.